Angermann, D., Seitz, M., Drewes, H., 2010, "Analysis of the DORIS contributions to ITRF2008," Advances in Space Research, 46, 1633-1647.

 

       In its function as an ITRS Combination Centre, DGFI is in charge with the computation of an ITRF2008 solution. The computation methodology of DGFI is based on the combination of datum-free normal equations (weekly or session data sets, respectively) of station positions and Earth orientation parameters (EOP) from the geodetic space techniques DORIS, GPS, SLR and VLBI. In this paper we focus on the DORIS part within the ITRF2008 computations. We present results obtained from the analysis of the DORIS time series for station positions, network translation and scale parameters, as well as for the terrestrial pole coordinates. The submissions to ITRF2008 benefit from improved analysis strategies of the seven contributing IDS analysis centres and from a combination of the weekly solutions of station positions and polar motion. The results show an improvement by a factor of two compared to past DORIS data submitted to ITRF2005, which has been evaluated by investigating the repeatabilities of position time series. The DORIS position time series were analysed w.r.t. discontinuities and other non-linear effects such as seasonal variations. About 40 discontinuities have been identified which have been compared with the results of an earlier study. Within the inter-technique combination we focus on the DORIS contribution to the integration of the different space geodetic observations and on a comparison of the geodetic local ties with the space geodetic solutions. Results are given for the 41 co-location sites between DORIS and GPS.

 

 

Archinal, B.A., A'Hearn, M.F., Bowell, E., Conrad, A., Consolmagno, G.J., Courtin, R., Fukushima, T., Hestroffer, D., Hilton, J.L., Krasinsky, G.A., Neumann, G., Oberst, J., Seidelmann, P.K., Stooke, P., Tholen, D.J., Thomas, P.C., Williams, I.P., 2010, "Report of the IAU Working Group on Cartographic Coordinates and Rotational Elements: 2009," Celestial Mechanics and Dynamical Astronomy, 89.

 

       Every three years the IAU Working Group on Cartographic Coordinates and Rotational Elements revises tables giving the directions of the poles of rotation and the prime meridians of the planets, satellites, minor planets, and comets. This report takes into account the IAU Working Group for Planetary System Nomenclature (WGPSN) and the IAU Committee on Small Body Nomenclature (CSBN) definition of dwarf planets, introduces improved values for the pole and rotation rate of Mercury, returns the rotation rate of Jupiter to a previous value, introduces improved values for the rotation of five satellites of Saturn, and adds the equatorial radius of the Sun for comparison. It also adds or updates size and shape information for the Earth, Mars' satellites Deimos and Phobos, the four Galilean satellites of Jupiter, and 22 satellites of Saturn. Pole, rotation, and size information has been added for the asteroids (21) Lutetia, (511) Davida, and (2867) .teins. Pole and rotation information has been added for (2) Pallas and (21) Lutetia. Pole and rotation and mean radius information has been added for (1) Ceres. Pole information has been updated for (4) Vesta. The high precision realization for the pole and rotation rate of the Moon is updated. Alternative orientation models for Mars, Jupiter, and Saturn are noted. The Working Group also reaffirms that once an observable feature at a defined longitude is chosen, a longitude definition origin should not change except under unusual circumstances. It is also noted that alternative coordinate systems may exist for various (e.g. dynamical) purposes, but specific cartographic coordinate system information continues to be recommended for each body. The Working Group elaborates on its purpose, and also announces its plans to occasionally provide limited updates to its recommendations via its website, in order to address community needs for some updates more often than every 3 years. Brief recommendations are also made to the general planetary community regarding the need for controlled products, and improved or consensus rotation models for Mars, Jupiter, and Saturn.

 

 

Aubert, J., Dumberry, M., 2011, "Steady and fluctuating inner core rotation in numerical geodynamo models," Geophysical Journal International, 184, 162-170.

 

       We present a systematic survey of numerical geodynamo simulations where the inner core is allowed to differentially rotate in the longitudinal direction with respect to the mantle. We focus on the long-term behaviour of inner core rotation, on timescales much longer than the overturn time of the fluid outer core, including the steady component of rotation. The inner core is subject to viscous and magnetic torques exerted by the fluid outer core, and a gravitational restoring torque exerted by the mantle. We show that the rate of steady inner core rotation is limited by the differential rotation between spherical surfaces that the convective dynamics can sustain across the fluid outer core. We further show that this differential rotation is determined by a torque balance between the resistive Lorentz force and the Coriolis force on spherical surfaces within the fluid core. We derive a scaling law on the basis of this equilibrium suggesting that the ratio of the steady inner core rotation to typical angular velocity within the fluid core should be proportional to the square root of the Ekman number, in agreement with our numerical results. The addition of gravitational coupling does not alter this scaling, though it further reduces the amplitude of inner core rotation. In contrast, the long-term fluctuations in inner core rotation remain proportional to the fluid core angular velocity, with no apparent dependency on the Ekman number. If the same torque balance pertains to the Earth's core conditions, the inner core rotation then consists in a very slow super rotation of a few degrees per million years, superimposed over large fluctuations (at about a tenth of a degree per year). This suggests that the present-day seismically inferred inner core rotation is a fragment of a time-varying signal, rather than a steady super rotation. For the inner core rotation fluctuations not to cause excessive variations in the length-of-day, the strength of the gravitational coupling between the inner core and the mantle must be smaller than previously published values. We finally explore how the torque balance which we observe in our models could be altered in planetary cores, yielding possibly larger values of the steady rotation.

 

 

Banzatti, A., Testi, L., Isella, A., Natta, A., Neri, R., Wilner, D.J., 2011, "New constraints on dust grain size and distribution in CQ Tauri," Astronomy and Astrophysics, 525, 12.

 

       Context. Grain growth in circumstellar disks is expected to be the first step towards the formation of planetary systems. There is now evidence for grain growth in several disks around young stars.

 

Aims: Radially resolved images of grain growth in circumstellar disks are believed to be a powerful tool to constrain the dust evolution models and the initial stage for the formation of planets. In this paper we attempt to provide these constraints for the disk surrounding the young star CQ Tau. This system was already suggested from previous studies to host a population of grains grown to large sizes.

 

Methods: We present new high angular resolution (0.3"-0.9") observations at wavelengths from 850 ?m to 3.6 cm obtained at the SMA, IRAM-PdBI and NRAO-VLA interferometers. We perform a combined analysis of the spectral energy distribution and of the high-resolution images at different wavelengths using a model to describe the dust thermal emission from the circumstellar disk. We include a prescription for the gas emission from the inner regions of the system.

 

Results: We detect the presence of evolved dust by constraining the disk averaged dust opacity coefficient b (computed between 1.3 and 7 mm) to be 0.6±0.1. This confirms the earlier suggestions that the disk contains dust grains grown to significant sizes and puts this on firmer grounds by tightly constraining the gas contamination to the observed fluxes at mm-cm wavelengths. We report some evidence of radial variations in dust properties, but current resolution and sensitivity are still too low for definitive results.

 

 

Barnes, R., Greenberg, R., Quinn, T.R., McArthur, B.E., Benedict, G.F., 2011, "Origin and Dynamics of the Mutually Inclined Orbits of u Andromedae c and d," The Astrophysical Journal, 726, 71.

 

       We evaluate the orbital evolution and several plausible origin scenarios for the mutually inclined orbits of u And c and d. These two planets have orbital elements that oscillate with large amplitudes and lie close to the stability boundary. This configuration, and in particular the observed mutual inclination, demands an explanation. The planetary system may be influenced by a nearby low-mass star, u And B, which could perturb the planetary orbits, but we find it cannot modify two coplanar orbits into the observed mutual inclination of 30°. However, it could incite ejections or collisions between planetary companions that subsequently raise the mutual inclination to >30°. Our simulated systems with large mutual inclinations tend to be further from the stability boundary than u And, but we are able to produce similar systems. We conclude that scattering is a plausible mechanism to explain the observed orbits of u And c and d, but we cannot determine whether the scattering was caused by instabilities among the planets themselves or by perturbations from u And B. We also develop a procedure to quantitatively compare numerous properties of the observed system to our numerical models. Although we only implement this procedure to ? And, it may be applied to any exoplanetary system.

 

 

Beaulieu, J.P., Kipping, D.M., Batista, V., Tinetti, G., Ribas, I., Carey, S., Noriega-Crespo, J.A., Griffith, C.A., Campanella, G., Dong, S., Tennyson, J., Barber, R.J., Deroo, P., Fossey, S.J., Liang, D., Swain, M.R., Yung, Y., Allard, N., 2010, "Water in the atmosphere of HD 209458b from 3.6-8 Beaulieu mm IRAC photometric observations in primary transit," Monthly Notices of the Royal Astronomical Society, 409, 963-974.

 

       The hot Jupiter HD 209458b was observed during primary transit at 3.6, 4.5, 5.8 and 8.0 mm using the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. We describe the procedures we adopted to correct for the systematic effects present in the IRAC data and the subsequent analysis. The light curves were fitted including limb-darkening effects and fitted using Markov Chain Monte Carlo and prayer-bead Monte Carlo techniques, obtaining almost identical results. The final depth measurements obtained by a combined Markov Chain Monte Carlo fit are at 3.6 mm, 1.469 ± 0.013 and 1.448 ± 0.013 per cent; at 4.5 mm, 1.478 ± 0.017 per cent; at 5.8 mm, 1.549 ± 0.015 per cent; and at 8.0 mm, 1.535 ± 0.011 per cent. Our results clearly indicate the presence of water in the planetary atmosphere. Our broad-band photometric measurements with IRAC prevent us from determining the additional presence of other molecules such as CO, CO2 and methane for which spectroscopy is needed. While water vapour with a mixing ratio of ? combined with thermal profiles retrieved from the day side may provide a very good fit to our observations, this data set alone is unable to resolve completely the degeneracy between water abundance and atmospheric thermal profile.

 

 

Beerer, I.M., Knutson, H.A., Burrows, A., Fortney, J.J., Agol, E., Charbonneau, D., Cowan, N.B., Deming, D., Desert, J.-M., Langton, J., Laughlin, G., Lewis, N.K., Showman, A.P., 2011, "Secondary Eclipse Photometry of WASP-4b with Warm Spitzer," The Astrophysical Journal, 727, 23.

 

       We present photometry of the giant extrasolar planet WASP-4b at 3.6 and 4.5 mm taken with the Infrared Array Camera on board the Spitzer Space Telescope as part of Spitzer's extended warm mission. We find secondary eclipse depths of 0.319% ± 0.031% and 0.343% ± 0.027% for the 3.6 and 4.5 mm bands, respectively, and show model emission spectra and pressure-temperature profiles for the planetary atmosphere. These eclipse depths are well fit by model emission spectra with water and other molecules in absorption, similar to those used for TrES-3 and HD 189733b. Depending on our choice of model, these results indicate that this planet has either a weak dayside temperature inversion or no inversion at all. The absence of a strong thermal inversion on this highly irradiated planet is contrary to the idea that highly irradiated planets are expected to have inversions, perhaps due the presence of an unknown absorber in the upper atmosphere. This result might be explained by the modestly enhanced activity level of WASP-4b's G7V host star, which could increase the amount of UV flux received by the planet, therefore reducing the abundance of the unknown stratospheric absorber in the planetary atmosphere as suggested in Knutson et al. We also find no evidence for an offset in the timing of the secondary eclipse and place a 2s upper limit on |ecos w| of 0.0024, which constrains the range of tidal heating models that could explain this planet's inflated radius.

 

 

Belu, A.R., Selsis, F., Morales, J.-C., Ribas, I., Cossou, C., Rauer, H., 2011, "Primary and secondary eclipse spectroscopy with JWST: exploring the exoplanet parameter space," Astronomy and Astrophysics, 525, 83.

 

       Context. During the past few years, eclipse exoplanet spectroscopy has enabled the detection of H2O, CH4, CO2, and CO in the atmosphere of hot Jupiters and Neptunes. At the same time, ~40 likely large terrestrial planets are announced or confirmed. Two of these are transiting, and another is deemed habitable. Therefore the potential for eclipse spectroscopy of terrestrial planets with the James Webb Space Telescope (JWST) has become an active field of study.

 

Aims: We aim to extensively explore the parameter space (type of stars, planet orbital periods, planet types, and instruments/wavelengths) in terms of signal-to-noise ratio (S/N) of the detection of spectroscopic features with the JWST. We also wish to confront the information on the S/N to the likelihood of occurring targets.

 

Methods: We used analytic formula and model data for both the astrophysical scene and the instrument to plot S/N contour maps, while indicating how the S/N scales with the fixed parameters. We systematically compare stellar photon noise-only plots with plots that include detailed instrumental and zodiacal noises. The likelihood of targets is based on both model and catalog star populations of the solar neighborhood

 

Results: The 9.6 mm ozone band is detectable (S/N = 3) with JWST, for a warm super earth 6.7 pc away, using ~2% of the 5-year nominal mission time (summing observations, M4 V and lighter host star for primary eclipses, M5 V for secondary). If every star up to this mass limit and distance were to host a habitable planet, there would be statistically a little under one eclipsing case. We also show that detection in transmission of the 2.05 mm CO2 feature on the 6.5 MEarth exoplanet GJ 1214 b is feasible with the Hubble Space Telescope (HST). For the low and the high bounds of the likely atmospheric mean molecular weight, just one eclipse or the whole HST yearly visibility window (107 days) is required.

 

Conclusions: It is critical to investigate systematic noises resulting from co-adding hours-long observations separated by tens of days, over a 5 year span. It is also critical to perform a dedicated characterization of the instruments, currently in integration phase. The census of nearby transiting habitable planets must be complete before JWST's science operations start.

 

 

Bodewits, D., Villanueva, G.L., Mumma, M.J., Landsman, W.B., Carter, J.A., Read, A.M., 2011, "Swift-UVOT Grism Spectroscopy of Comets: A First Application to C/2007 N3 (Lulin)," The Astronomical Journal, 141, 12.

 

       We observed comet C/2007 N3 (Lulin) twice on UT 2009 January 28, using the UV grism of the Ultraviolet and Optical Telescope on board the Swift gamma-ray burst space observatory. Grism spectroscopy provides spatially resolved spectroscopy over large apertures for faint objects. We developed a novel methodology to analyze grism observations of comets, and applied a Haser comet model to extract production rates of OH, CS, NH, CN, C3, C2, and dust. The water production rates retrieved from two visits on this date were 6.7 ± 0.7 and 7.9 ± 0.7 ×1028 molecules s.1, respectively. Jets were sought (but not found) in the white-light and "OH" images reported here, suggesting that the jets reported by Knight & Schleicher are unique to CN. Based on the abundances of its carbon-bearing species, comet Lulin is "typical" (i.e., not "depleted") in its composition.

 

 

Bouchy, F., Deleuil, M., Guillot, T., Aigrain, S., Carone, L., Cochran, W.D., Almenara, J.M., Alonso, R., Auvergne, M., Baglin, A., Barge, P., Bonomo, A.S., BordéP., Csizmadia, S., de Bondt, K., Deeg, H.J., Dí, R.F., Dvorak, R., Endl, M., Erikson, A., Ferraz-Mello, S., Fridlund, M., Gandolfi, D., Gazzano, J.C., Gibson, N., Gillon, M., Guenther, E., Hatzes, A., Havel, M., Héard, G., Jorda, L., Lér, A., Lovis, C., Llebaria, A., Lammer, H., MacQueen, P.J., Mazeh, T., Moutou, C., Ofir, A., Ollivier, M., Parviainen, H., Päold, M., Queloz, D., Rauer, H., Rouan, D., Santerne, A., Schneider, J., Tingley, B., Wuchterl, G., 2011, "Transiting exoplanets from the CoRoT space mission. XV. CoRoT-15b: a brown-dwarf transiting companion," Astronomy and Astrophysics, 525, 68.

 

       We report the discovery by the CoRoT space mission of a transiting brown dwarf orbiting a F7V star with an orbital period of 3.06 days. CoRoT-15b has a radius of 1.12+0.30-0.15 {R}Jup and a mass of 63.3 ± 4.1 {M}Jup, and is thus the second transiting companion lying in the theoretical mass domain of brown dwarfs. CoRoT-15b is either very young or inflated compared to standard evolution models, a situation similar to that of M-dwarf stars orbiting close to solar-type stars. Spectroscopic constraints and an analysis of the lightcurve imply a spin period in the range 2.9-3.1 days for the central star, which is compatible with a double-synchronisation of the system.

 

 

Cambiotti, G., Ricard, Y., Sabadini, R., 2010, "Ice age True Polar Wander in a compressible and non-hydrostatic Earth," Geophysical Journal International, 183, 1248-1264.

 

       Issues related to long timescale instability in the Earth's rotation, named True Polar Wander (TPW), have continuously been debated, after the pioneering works of the sixties. We show ice age TPW results from a newly developed compressible model, based on the numerical integration in the radial variable of the momentum and Poisson equations and on the contour integration in the Laplace domain which allows us to deal with the non-modal contribution from continuous radial rheological variations. We thus fully exploit the long term behaviour of the Earth's rotation and we quantify the effects of the compressible rheology, compared to the widely used incompressible one. We discuss the so-called `traditional approach' to the Earth's rotation developed during the eighties and nineties, both for ice age and mantle convection TPW and we explain within this approach the sensitivity of TWP predictions to the elastic and viscoelastic rheologies of the lithosphere. We agree on the necessity to include the effects of the non-hydrostatic bulge from mantle convection to obtain realistic ice age TPW rates in the lower mantle viscosity range [1021, 1022] Pa s, as first indicated by Mitrovica et al. Their analysis represents a first attempt to couple the effects on TPW from mantle convection and glacial forcing, by including the non-hydrostatic bulge due to mantle convection but not the other time-dependent driving terms. This partial coupling freezes in space the non-hydrostatic contribution due to mantle convection, thus damping the present-day ice age TPW and forcing the axis of instantaneous rotation to come back to its initial position when ice ages started as discussed in Mitrovica et al. We also describe a peculiar behavior of the new ice age TPW predictions exhibiting a dampened pendulum motion, with the axis of instantaneous rotation overcrossing the position it had before ice ages started. We argue that a viscoelastic rather than elastic lithosphere should be adopted in the modelling of TPW although, on the time of ice ages, it is difficult to disentangle the effects of lithospheric rheology and of mantle convection. We discuss the implication of self-consistent convection calculations of the non-hydrostatic contribution and its impact on the long term Earth's rotation stability during ice ages. The ice age TPW cannot account for more than 70 per cent of the observed one, at least for lower mantle viscosities lower than 1022 Pa s: mantle convection must therefore contribute to the observed TPW.

 

Christiansen, J.L., Ballard, S., Charbonneau, D., Deming, D., Holman, M.J., Madhusudhan, N., Seager, S., Wellnitz, D.D., Barry, R.K., Livengood, T.A., Hewagama, T., Hampton, D.L., Lisse, C.M., A'Hearn, M.F., 2011, "System Parameters, Transit Times, and Secondary Eclipse Constraints of the Exoplanet Systems HAT-P-4, TrES-2, TrES-3, and WASP-3 from the NASA EPOXI Mission of Opportunity," The Astrophysical Journal, 726, 94.

 

As part of the NASA EPOXI Mission of Opportunity, we observed seven known transiting extrasolar planet systems in order to construct time series photometry of extremely high phase coverage and precision. Here we present the results for four "hot-Jupiter systems" with near-solar stars.HAT-P-4, TrES-3, TrES-2, and WASP-3. We observe 10 transits of HAT-P-4, estimating the planet radius Rp = 1.332 ± 0.052 RJup, the stellar radius Rêspan>= 1.602 ± 0.061 RSun, the inclination i = 89.67 ± 0.30 deg, and the transit duration from first to fourth contact t = 255.6 ± 1.9 minutes. For TrES-3, we observe seven transits and find Rp = 1.320 ± 0.057 RJup, Rêspan>= 0.817 ± 0.022 RSun, i = 81.99 ± 0.30 deg, and t = 81.9 ± 1.1 minutes. We also note a long-term variability in the TrES-3 light curve, which may be due to star spots. We observe nine transits of TrES-2 and find Rp = 1.169 ± 0.034 RJup, Rêspan>= 0.940 ± 0.026 RSun, i = 84.15 ± 0.16 deg, and t = 107.3 ± 1.1 minutes. Finally, we observe eight transits of WASP-3, finding Rp = 1.385 ± 0.060 RJup, Rêspan>= 1.354 ± 0.056 RSun, i = 84.22 ± 0.81 deg, and t = 167.3 ± 1.3 minutes. We present refined orbital periods and times of transit for each target. We state 95% confidence upper limits on the secondary eclipse depths in our broadband visible bandpass centered on 650 nm. These limits are 0.073% for HAT-P-4, 0.062% for TrES-3, 0.16% for TrES-2, and 0.11% for WASP-3. We combine the TrES-3 secondary eclipse information with the existing published data and confirm that the atmosphere likely does not have a temperature inversion.

 

 

Curiel, S., Cantó., Georgiev, L., Cház, C.E., Poveda, A., 2011, "A fourth planet orbiting u Andromedae," Astronomy and Astrophysics, 525, 78.

 

We present a 4-planet Keplerian fit for the radial velocity curve of the F8V star ? Andromeda, indicating the presence of a fourth planet in the system. We detect an additional fifth coherent signal in the radial velocity curve which we attribute to stellar activity. The discovery of a new planet around u Andromedae makes this system the fifth to contain, at least, four planets. These four planets have minimum masses of 0.69, 1.98, 4.13 and 1.06 MJup and orbital periods of 4.62, 241.26, 1276.46 and 3848.9 days, respectively. We have numerically integrated the orbital solution for these four planets and find that the system is stable for at least 10 Myr. The orbit of the fourth planet coincides with an island of stability reported by Rivera & Haghighipour (2007, MNRAS, 374, 599). We find that the characteristics of the new fourth planet are very similar to those of Jupiter and that the planets in this system have very strong interactions with each other. As previously found, u And-b and u And-c are in apsidal alignment, while the orbit of the new planet (u And-e) is close to an external 3:1 resonance with u And-c.

 

Deming, D., Knutson, H., Agol, E., Desert, J.-M., Burrows, A., Fortney, J.J., Charbonneau, D., Cowan, N.B., Laughlin, G., Langton, J., Showman, A.P., Lewis, N.K., 2011, "Warm Spitzer Photometry of the Transiting Exoplanets CoRoT-1 and CoRoT-2 at Secondary Eclipse," The Astrophysical Journal, 726, 95.

 

We measure secondary eclipses of the hot giant exoplanets CoRoT-1 at 3.6 and 4.5 mm, and CoRoT-2 at 3.6 mm, both using Warm Spitzer. We find that the Warm Spitzer mission is working very well for exoplanet science. For consistency of our analysis we also re-analyze archival cryogenic Spitzer data for secondary eclipses of CoRoT-2 at 4.5 and 8 mm. We compare the total data for both planets, including optical eclipse measurements by the CoRoT mission, and ground-based eclipse measurements at 2 mm, to existing models. Both planets exhibit stronger eclipses at 4.5 than at 3.6 mm, which is often indicative of an atmospheric temperature inversion. The spectrum of CoRoT-1 is best reproduced by a 2460 K blackbody, due either to a high altitude layer that strongly absorbs stellar irradiance, or an isothermal region in the planetary atmosphere. The spectrum of CoRoT-2 is unusual because the 8 mm contrast is anomalously low. Non-inverted atmospheres could potentially produce the CoRoT-2 spectrum if the planet exhibits line emission from CO at 4.5 mm, caused by tidal-induced mass loss. However, the viability of that hypothesis is questionable because the emitting region cannot be more than about 30% larger than the planet's transit radius, based on the ingress and egress times at eclipse. An alternative possibility to account for the spectrum of CoRoT-2 is an additional opacity source that acts strongly at wavelengths less than 5 mm, heating the upper atmosphere while allowing the deeper atmosphere seen at 8 mm to remain cooler. We obtain a similar result as Gillon et al. for the phase of the secondary eclipse of CoRoT-2, implying an eccentric orbit with e cos(w) = .0.0030 ± 0.0004.

 

 

Dickman, S.R., 2010, "Rotationally acceptable ocean tide models for determining the response of the oceans to atmospheric pressure fluctuations," Journal of Geophysical Research (Solid Earth), 115, 12407.

 

Suitably generalized, ocean tide models can be used to determine the oceans' response to atmospheric pressure forcing; but the huge range of spatial and temporal scales of that forcing limits the relevance of state-of-the-art tide modeling techniques, like data assimilation, for such determinations. With an interest in its effects on Earth's rotation, in 1998 I employed a generalized but non-assimilating spherical harmonic tide model to determine the oceanic response to pressure forcing, however restricting its application to time scales exceeding a few days. This article revisits that spherical harmonic model in an attempt to improve its rotational predictions of short-period tides. We find that increasing the resolution of the model ocean does not by itself affect the tidal solution much, but varying the model's frictional parameters can produce diurnal tides whose effects on Earth's polar motion are similar to those of a variety of other ocean tide models. Such an improved model will allow our calculations of the oceans' dynamic response to pressure forcing, and the effects of that response on Earth's rotation, to be extended down to diurnal time scales.

 

 

Dodson-Robinson, S.E., Beichman, C.A., Carpenter, J.M., Bryden, G., 2011, "A Spitzer Infrared Spectrograph Study of Debris Disks Around Planet-host Stars," The Astronomical Journal, 141, 11.

 

       Since giant planets scatter planetesimals within a few tidal radii of their orbits, the locations of existing planetesimal belts indicate regions where giant planet formation failed in bygone protostellar disks. Infrared observations of circumstellar dust produced by colliding planetesimals are therefore powerful probes of the formation histories of known planets. Here we present new Spitzer infrared spectrograph (IRS) spectrophotometry of 111 solar-type stars, including 105 planet hosts. Our observations reveal 11 debris disks, including two previously undetected debris disks orbiting HD 108874 and HD 130322. Combining the 32 mm spectrophotometry with previously published MIPS photometry, we find that the majority of debris disks around solar-type stars have temperatures in the range 60 <~ Tdust <~ 100 K. Assuming a dust temperature Tdust = 70 K, which is representative of the nine debris disks detected by both IRS and MIPS, debris rings surrounding Sun-like stars orbit between 15 and 240 AU depending on the mean particle size. Our observations imply that the planets detected by radial-velocity searches formed within 240 AU of their parent stars. If any of the debris disks studied here have mostly large, blackbody emitting grains, their companion giant planets must have formed in a narrow region between the ice line and 15 AU.

 

 

Dumusque, X., Udry, S., Lovis, C., Santos, N.C., Monteiro, M.J.P.F.G., 2011, "Planetary detection limits taking into account stellar noise. I. Observational strategies to reduce stellar oscillation and granulation effects," Astronomy and Astrophysics, 525, 140.

 

Context. Stellar noise produced by oscillations, granulation phenomena (granulation, mesogranulation, and supergranulation), and activity affects radial velocity measurements. The signature of the corresponding effect in radial velocity is small, around the meter-per-second, but already too large for the detection of Earth-mass planets in habitable zones.

 

Aims: We address the important role played by observational strategies in averaging out the radial velocity signature of stellar noise. We also derive the planetary mass detection limits expected in the presence of stellar noise.

 

Methods: We start with HARPS asteroseismology measurements for four stars (b Hyi, a Cen A, m Ara, and t Ceti) available in the ESO archive and very precise measurements of a Cen B. This sample covers different spectral types from G2 to K1 and different evolutionary stages, from subgiant to dwarf stars. Since data span between 5 and 8 days, only stellar noise sources with timescales shorter than this time span will be extracted from these observations. Therefore, we are able to study oscillation modes and granulation phenomena without being significantly affected by activity noise present on longer timescales. For those five stars, we generate synthetic radial velocity measurements after fitting the corresponding models of stellar noise in Fourier space. These measurements allow us to study the radial velocity variation due to stellar noise for different observational strategies as well as the corresponding planetary mass detection limits.

 

Results: Applying three measurements per night of 10 min exposure each, 2 h apart, seems to most efficiently average out the stellar noise considered. For quiet K1V stars such as a Cen B, this strategy allows us to detect planets of about three times the mass of Earth with an orbital period of 200 days, corresponding to the habitable zone of the star. Moreover, our simulations suggest that planets smaller than typically 5 MEarth can be detected with HARPS over a wide range of separations around most non-active solar-type dwarfs. Since activity is not yet included in our simulation, these detection limits correspond to a case, which exists, where the host star has few magnetic features and stellar noise is dominated by oscillation modes and granulation phenomena. For our star sample, a trend between spectral type and surface gravity and the level of radial velocity variation is also identified by our simulations

 

Eibe, M.T., Cuesta, L., Ullá A., Péz-Verde, A., Navas, J., 2010, "High-precision automated follow-up transit photometry with a 50-cm robotic telescope," Monthly Notices of the Royal Astronomical Society, 1855.

 

We present the first results from long-term photometric observations carried out with the INTA-CAB 50-cm telescope in a fully robotic mode. The data belong to an ongoing programme for the photometric follow up of known transiting close-in giant planets. We describe the techniques used to generate differential light curves of the programme stars and discuss the photometric performance obtained over the first year of operation.

 

 

 

Emery, J.P., Burr, D.M., Cruikshank, D.P., 2011, "Near-infrared Spectroscopy of Trojan Asteroids: Evidence for Two Compositional Groups," The Astronomical Journal, 141, 25.

 

The Trojan asteroids, a very substantial population of primitive bodies trapped in Jupiter's stable Lagrange regions, remain quite poorly understood. Because they occupy these orbits, the physical properties of Trojans provide a unique perspective on the chemical and dynamical processes that shaped the Solar System. The current study was therefore undertaken to investigate surface compositions of these objects. We present 66 new near-infrared (NIR; 0.7-2.5 ?m) spectra of 58 Trojan asteroids, including members of both the leading and trailing swarms. We also include in the analysis previously published NIR spectra of 13 Trojans (3 of which overlap with the new sample). This data set permits not only a direct search for compositional signatures, but also a search for patterns that may reveal clues to the origin of the Trojans. We do not report any confirmed absorption features in the new spectra. Analysis of the spectral slopes, however, reveals an interesting bimodality among the NIR data. The two spectral groups identified appear to be equally abundant in the leading and trailing swarms. The spectral groups are not a result of family membership; they occur in the background, non-family population. The average albedos of the two groups are the same within uncertainties (0.051 ± 0.016 and 0.055 ± 0.016). No correlations between spectral slope and any other physical or orbital parameter are detected, with the exception of a possible weak correlation with inclination among the less-red spectral group. The NIR spectral groups are consistent with a similar bimodality previously suggested among visible colors and spectra. Synthesizing the present results with previously published properties of Trojans, we conclude that the two spectral groups represent objects with different intrinsic compositions. We further suggest that whereas the less-red group originated near Jupiter or in the main asteroid belt, the redder spectral group originated farther out in the Solar System. If this suggestion is correct, the Trojan swarms offer the most readily accessible large reservoir of Kuiper Belt material as well as a unique reservoir for the study of material from the middle part of the solar nebula.

 

 

Faedi, F., West, R.G., Burleigh, M.R., Goad, M.R., Hebb, L., 2011, "Detection limits for close eclipsing and transiting substellar and planetary companions to white dwarfs in the WASP survey," Monthly Notices of the Royal Astronomical Society, 410, 899-911.

 

       We have performed extensive simulations to explore the possibility of detecting eclipses and transits of close, substellar and planetary companions to white dwarfs in WASP (the UK Wide-Angle Search for Planets) light curves. Our simulations cover companions ~0.3 < Rpl < 12 REarth and orbital periods 2 < P < 15 d, equivalent to orbital radii 0.003 < a < 0.1 au. For Gaussian random noise, WASP is sensitive to transits by companions as small as the Moon orbiting a V ~= 12 white dwarf. For fainter white dwarfs, WASP is sensitive to increasingly larger radius bodies. However, in the presence of correlated noise structure in the light curves, the sensitivity drops, although Earth-sized companions remain detectable, in principle, even in low signal-to-noise data. Mars-sized, and even Mercury-sized, bodies yield reasonable detection rates in high-quality light curves with little residual noise. We searched for eclipses and transit signals in long-term light curves of a sample of 194 white dwarfs resulting from a cross-correlation of the McCook & Sion catalogue and the WASP archive. No evidence for eclipsing or transiting substellar and planetary companions was found. We used this non-detection and results from our simulations to place tentative upper limits to the frequency of such objects in close orbits at white dwarfs. While only weak limits can be placed on the likely frequency of Earth-sized or smaller companions, brown dwarfs and gas giants (radius ≈ RJup) with periods <0.1-0.2 d must certainly be rare (<10 per cent). More stringent constraints likely require significantly larger white dwarf samples, higher observing cadence and continuous coverage. The short duration of eclipses and transits of white dwarfs compared to the cadence of WASP observations appears to be one of the main factors limiting the detection rate in a survey optimized for planetary transits of main-sequence stars.

 

 

Funk, B., Schwarz, R., Dvorak, R., Roth, M., 2011, "Exchange orbits: a possible application to extrasolar planetary systems?," Monthly Notices of the Royal Astronomical Society, 410, 455-460.

 

Among the 48 known multiplanetary systems, some are in mean-motion resonances (in most cases in the 2:1 mean-motion resonance). Although until now no extrasolar planetary systems have been found in a 1:1 mean-motion resonance, many studies are dealing with this configuration. Besides the well-known motion of the Trojan asteroids, further possibilities exist for stable configurations of planets or satellites in a 1:1 resonance. For one thing, we can find so-called exchange orbits in our Solar system (Janus and Epimetheus), where both Saturnian moons exchange the values of their semi-major axes (exchange-a configuration) when approaching each other. In addition, we can also find similar behaviour for two planets on orbits with the same semi-major axis, but with different eccentricities; here an exchange of eccentricities takes place (exchange-e configuration). In this work we focused on the second possibility and performed a parameter study by varying the initial conditions (mass and eccentricity) of two planets on exchange-e orbits. By means of an extensive numerical study, we can find a wide variety of initial conditions leading to long-term stable orbits.

 

 

Gabryszewski, R., Rickman, H., 2010, "On the Dynamical Evolution of Scattered Disk Objects Outside the Planetary System," Acta Astronomica, 60, 373-385.

 

We report the results of dynamical simulations, covering Gyr timescales, of fictitious Scattered Disk Objects as a follow-up to an earlier study. Our dynamical model is similar in that it does not include external agents like passing stars or the Galactic tide. Only the four giant planets are explicitly treated as perturbers. We analyze the random-walk behavior of the inverse semi-major axis by means of a simplified circular restricted 3-body problem as an approximate analogue. Our results concerning the role of resonant effects and the transfer efficiency into the orbital energy domain of the inner Oort Cloud are in broad agreement with the earlier papers, and we confirm the important role of external objects (with perihelia beyond Neptune's orbit) in feeding the Oort Cloud. We estimate the efficiency of this transfer to be even somewhat higher than previously found.

 

 

Gandolfi, D., Héard, G., Alonso, R., Deleuil, M., Guenther, E.W., Fridlund, M., Endl, M., Eigmü P., Csizmadia, S., Havel, M., Aigrain, S., Auvergne, M., Baglin, A., Barge, P., Bonomo, A.S., BordéP., Bouchy, F., Bruntt, H., Cabrera, J., Carpano, S., Carone, L., Cochran, W.D., Deeg, H.J., Dvorak, R., Eislöl, J., Erikson, A., Ferraz-Mello, S., Gazzano, J.-C., Gibson, N.B., Gillon, M., Gondoin, P., Guillot, T., Hartmann, M., Hatzes, A., Jorda, L., Kabath, P., Lér, A., Llebaria, A., Lammer, H., MacQueen, P.J., Mayor, M., Mazeh, T., Moutou, C., Ollivier, M., Päold, M., Pepe, F., Queloz, D., Rauer, H., Rouan, D., Samuel, B., Schneider, J., Stecklum, B., Tingley, B., Udry, S., Wuchterl, G., 2010, "Transiting exoplanets from the CoRoT space mission. XIV. CoRoT-11b: a transiting massive ``hot-Jupiter'' in a prograde orbit around a rapidly rotating F-type star," Astronomy and Astrophysics, 524, 55.

 

The CoRoT exoplanet science team announces the discovery of CoRoT-11b, a fairly massive hot-Jupiter transiting a V = 12.9 mag F6 dwarf star (M * = 1.27±0.05 MSun, R* = 1.37±0.03 RSun, Teff = 6440±120 K), with an orbital period of P = 2.994329±0.000011 days and semi-major axis a = 0.0436±0.005 AU. The detection of part of the radial velocity anomaly caused by the Rossiter-McLaughlin effect shows that the transit-like events detected by CoRoT are caused by a planet-sized transiting object in a prograde orbit. The relatively high projected rotational velocity of the star (v sin i = 40±5 km s-1) places CoRoT-11 among the most rapidly rotating planet host stars discovered so far. With a planetary mass of Mp = 2.33±0.34 MJup and radius Rp =1.43±0.03 RJup, the resulting mean density of CoRoT-11b (rp = 0.99±0.15 g/cm3) can be explained with a model for an inflated hydrogen-planet with a solar composition and a high level of energy dissipation in its interior.

 

 

Gillon, M., Bonfils, X., Demory, B.-O., Seager, S., Deming, D., Triaud, A.H.M.J., 2011, "An educated search for transiting habitable planets:. Targetting M dwarfs with known transiting planets," Astronomy and Astrophysics, 525, 32.

 

Because the planets of a system form in a flattened disk, they are expected to share similar orbital inclinations at the end of their formation. The high-precision photometric monitoring of stars known to host a transiting planet could thus reveal the transits of one or more other planets. We investigate here the potential of this approach for the M dwarf GJ 1214 that hosts a transiting super-Earth. For this system, we infer the transit probabilities as a function of orbital periods. Using Monte-Carlo simulations we address both the cases for fully coplanar and for non-coplanar orbits, with three different choices of inclinations distribution for the non-coplanar case. GJ 1214 reveals to be a very promising target for the considered approach. Because of its small size, a ground-based photometric monitoring of this star could detect the transit of a habitable planet as small as the Earth, while a space-based monitoring could detect any transiting habitable planet down to the size of Mars. The mass measurement of such a small planet would be out of reach for current facilities, but we emphasize that a planet mass would not be needed to confirm the planetary nature of the transiting object. Furthermore, the radius measurement combined with theoretical arguments would help us to constrain the structure of the planet.

 

 

Goerdt, T., Moore, B., Read, J.I., Stadel, J., 2010, "Core Creation in Galaxies and Halos Via Sinking Massive Objects," The Astrophysical Journal, 725, 1707-1716.

 

We perform a detailed investigation into the disruption of central cusps via the transfer of energy from sinking massive objects. Constant density inner regions form at the radius where the enclosed mass approximately matches the mass of the infalling body. We explore parameter space using numerical simulations and give an empirical relation for the size of the resulting core within structures that have different initial cusp slopes. We find that infalling bodies always stall at the edge of these newly formed cores, experiencing no dynamical friction over many dynamical times. As applications, we consider the resulting decrease in the dark matter annihilation flux due to centrally destroyed cusps, and we present a new theory for the formation of close binary nuclei.the "stalled binary" model. We focus on one particularly interesting binary nucleus system, the dwarf spheroidal galaxy VCC 128 which is dark matter dominated at all radii. We show that its nuclei would rapidly coalesce within a few million years if it has a central dark matter cusp slope steeper than r -1. However, if its initial dark matter cusp is slightly shallower than a logslope of -0.75 at ~0.1% of the virial radius, then the sinking nuclei naturally create a core equal to their observed separation and stall. This is close to the logslope measured in a recent billion particle cold dark matter halo simulation.

 

 

Gorshkov, V.L., 2010, "Study of the interannual variations of the Earth's rotation," Solar System Research, 44, 487-497.

 

In this work we investigate the variations of the Earth's rotation in the interval of periods from 2 to 8 years using the longest available observational series obtained both by means of astrometry and space geodesy. We found an abrupt change of the variation pattern in the middle of the 1980s, when classical ground-based astrometric facilities for studying the Earth Rotation Parameters (ERP) were replaced with space geodesy methods. Variations with a 6-year periodicity and ~0.2-ms amplitude practically disappeared (space geodesy instruments did not detect these variations right from the start), but the 2- to 4-year periodicities increased in amplitude and began to dominate in this frequency range under consideration. In this study, we analyze some possible excitation sources and possible causes of the change in the variability pattern.

 

 

Gregory, P.C., 2011, "Bayesian exoplanet tests of a new method for MCMC sampling in highly correlated model parameter spaces," Monthly Notices of the Royal Astronomical Society, 410, 94-110.

 

       The Markov chain Monte Carlo (MCMC) method is a powerful technique for facilitating Bayesian non-linear model fitting. In many cases, the MCMC exploration of the parameter space is very inefficient, because the model parameters are highly correlated. Differential evolution MCMC is one technique that addresses this problem by employing multiple parallel chains. We present a new method that automatically achieves efficient MCMC sampling in highly correlated parameter spaces, which does not require additional chains to accomplish this. It was designed to work with an existing hybrid MCMC (HMCMC) algorithm, which incorporates parallel tempering, simulated annealing and genetic cross-over operations. These features, together with the new correlated parameter sampler, greatly facilitate the detection of a global minimum in c2. The new HMCMC algorithm is very general in scope. Two tests of the algorithm are described employing (a) exoplanet precision radial velocity (RV) data and (b) simulated space astrometry data. The latter test explores the accuracy of parameter estimates obtained with the Bayesian HMCMC algorithm on the assumed astrometric noise.

 

 

Guenther, E.W., Cabrera, J., Erikson, A., Fridlund, M., Lammer, H., Mura, A., Rauer, H., Schneider, J., Tulej, M., von Paris, P., Wurz, P., 2011, "Constraints on the exosphere of CoRoT-7b," Astronomy and Astrophysics, 525, 24.

 

Context. The small radius and high density of CoRoT-7b implies that this transiting planet belongs to a different species than all transiting planets previously found. Current models suggest that this is the first transiting rocky planet found outside the solar system. Given that the planet orbits a solar-like star at a distance of only 4.5 R *, it is expected that material released from its surface may then form an exosphere.

 

 Aims: We constrain the properties of the exosphere by observing the planet in- and out-of-transit. Detecting the exosphere of CoRoT-7b would for the first time allow us to study the material originating in the surface of a rocky extrasolar planet. We scan the entire optical spectrum for any lines originating from the planet, focusing particularly on spectral lines such as those detected in Mercury and Io in our solar system.

 

Methods: Since lines originating in the exosphere are expected to be narrow, we observed CoRoT-7b at high resolution with UVES on the VLT. By subtracting the two spectra from each other, we search for emission and absorption lines originating in the exosphere of CoRoT-7b.

 

Results: In the first step, we focus on Ca I, Ca II, and Na, because these lines have been detected in Mercury. Since the signal-to-noise ratio (S/N) of the spectra is as high as 300, we derive firm upper limits for the flux-range between 1.6 ×10-18  and 3.2 ×10-18  W m-2. For CaO, we find an upper limit of 10-17 W m-2.  We also search for emission lines originating in the plasma torus fed by volcanic activity and derive upper limits for these lines. In the whole spectrum we finally try to identify other lines originating in the planet.

 

Conclusions: Except for CaO, the upper limits derived correspond to 2-6×0-6 L *, demonstrating the capability of UVES to detect very weak lines. Our observations certainly exclude the extreme interpretations of data for CoRoT-7b, such as an exosphere that emits 2000 times as brightly as Mercury.

 

 

Hartman, J.D., Bakos, G.Á, Sato, B., Torres, G., Noyes, R.W., Latham, D.W., Ková, G., Fischer, D.A., Howard, A.W., Johnson, J.A., Marcy, G.W., Buchhave, L.A., Fü G., Perumpilly, G., Bé, B., Stefanik, R.P., Sasselov, D.D., Esquerdo, G.A., Everett, M., Csubry, Z., Lár, J., Papp, I., Sá, P., 2011, "HAT-P-18b and HAT-P-19b: Two Low-density Saturn-mass Planets Transiting Metal-rich K Stars," The Astrophysical Journal, 726, 52.

 

We report the discovery of two new transiting extrasolar planets. HAT-P-18b orbits the V = 12.759 K2 dwarf star GSC 2594.00646, with a period P = 5.508023 ± 0.000006 days, transit epoch Tc = 2454715.02174 ± 0.00020 (BJD), and transit duration 0.1131 ± 0.0009 days. The host star has a mass of 0.77 ± 0.03 M Sun, radius of 0.75 ± 0.04 R Sun, effective temperature 4803 ± 80 K, and metallicity [Fe/H] = +0.10 ± 0.08. The planetary companion has a mass of 0.197 ± 0.013 MJ and radius of 0.995 ± 0.052 RJ, yielding a mean density of 0.25 ± 0.04 g cm.3. HAT-P-19b orbits the V = 12.901 K1 dwarf star GSC 2283.00589, with a period P = 4.008778 ± 0.000006 days, transit epoch Tc  = 2455091.53417 ± 0.00034 (BJD), and transit duration 0.1182 ± 0.0014 days. The host star has a mass of 0.84 ± 0.04 M Sun, radius of 0.82 ± 0.05 R Sun, effective temperature 4990 ± 130 K, and metallicity [Fe/H] = +0.23 ± 0.08. The planetary companion has a mass of 0.292 ± 0.018 MJ and radius of 1.132 ± 0.072 RJ, yielding a mean density of 0.25 ± 0.04 g cm.3. The radial velocity residuals for HAT-P-19 exhibit a linear trend in time, which indicates the presence of a third body in the system. Comparing these observations with theoretical models, we find that HAT-P-18b and HAT-P-19b are each consistent with a hydrogen-helium-dominated gas giant planet with negligible core mass. HAT-P-18b and HAT-P-19b join HAT-P-12b and WASP-21b in an emerging group of low-density Saturn-mass planets, with negligible inferred core masses. However, unlike HAT-P-12b and WASP-21b, both HAT-P-18b and HAT-P-19b orbit stars with super-solar metallicity. This calls into question the heretofore suggestive correlation between the inferred core mass and host star metallicity for Saturn-mass planets

 

 

Hogg, D.W., Myers, A.D., Bovy, J., 2010, "Inferring the Eccentricity Distribution," The Astrophysical Journal, 725, 2166-2175.

 

Standard maximum-likelihood estimators for binary-star and exoplanet eccentricities are biased high, in the sense that the estimated eccentricity tends to be larger than the true eccentricity. As with most non-trivial observables, a simple histogram of estimated eccentricities is not a good estimate of the true eccentricity distribution. Here, we develop and test a hierarchical probabilistic method for performing the relevant meta-analysis, that is, inferring the true eccentricity distribution, taking as input the likelihood functions for the individual star eccentricities, or samplings of the posterior probability distributions for the eccentricities (under a given, uninformative prior). The method is a simple implementation of a hierarchical Bayesian model; it can also be seen as a kind of heteroscedastic deconvolution. It can be applied to any quantity measured with finite precision.other orbital parameters, or indeed any astronomical measurements of any kind, including magnitudes, distances, or photometric redshifts.so long as the measurements have been communicated as a likelihood function or a posterior sampling.

 

 

Howard, A.W., Johnson, J.A., Marcy, G.W., Fischer, D.A., Wright, J.T., Henry, G.W., Isaacson, H., Valenti, J.A., Anderson, J., Piskunov, N.E., 2011, "The NASA-UC Eta-Earth Program. II. A Planet Orbiting HD 156668 with a Minimum Mass of Four Earth Masses," The Astrophysical Journal, 726, 73.

 

We report the discovery of HD 156668 b, an extrasolar planet with a minimum mass of MPsin i = 4.15 MEarth. This planet was discovered through Keplerian modeling of precise radial velocities from Keck-HIRES and is the second super-Earth to emerge from the NASA-UC Eta-Earth Survey. The best-fit orbit is consistent with circular and has a period of P = 4.6455 days. The Doppler semi-amplitude of this planet, K = 1.89 m s.1, is among the lowest ever detected, on par with the detection of GJ 581 e using HARPS. A longer period (P ≈ 2.3 years), low-amplitude signal of unknown origin was also detected in the radial velocities and was filtered out of the data while fitting the short-period planet. Additional data are required to determine if the long-period signal is due to a second planet, stellar activity, or another source. Photometric observations using the Automated Photometric Telescopes at Fairborn Observatory show that HD 156668 (an old, quiet K3 dwarf) is photometrically constant over the radial velocity period to 0.1 mmag, supporting the existence of the planet. No transits were detected down to a photometric limit of ~3 mmag, ruling out transiting planets dominated by extremely bloated atmospheres, but not precluding a transiting solid/liquid planet with a modest atmosphere.

 

 

Howell, S.B., Rowe, J.F., Sherry, W., von Braun, K., Ciardi, D.R., Bryson, S.T., Feldmeier, J.J., Horch, E., van Belle, G.T., 2010, "Kepler Observations of Three Pre-launch Exoplanet Candidates: Discovery of Two Eclipsing Binaries and a New Exoplanet," The Astrophysical Journal, 725, 1633-1643.

 

       Three transiting exoplanet candidate stars were discovered in a ground-based photometric survey prior to the launch of NASA's Kepler mission. Kepler observations of them were obtained during Quarter 1 of the Kepler mission. All three stars are faint by radial velocity follow-up standards, so we have examined these candidates with regard to eliminating false positives and providing high confidence exoplanet selection. We present a first attempt to exclude false positives for this set of faint stars without high-resolution radial velocity analysis. This method of exoplanet confirmation will form a large part of the Kepler mission follow-up for Jupiter-sized exoplanet candidates orbiting faint stars. Using the Kepler light curves and pixel data, as well as medium-resolution reconnaissance spectroscopy and speckle imaging, we find that two of our candidates are binary stars. One consists of a late-F star with an early M companion, while the other is a K0 star plus a late M-dwarf/brown dwarf in a 19 day elliptical orbit. The third candidate (BOKS-1) is an r = 15 G8V star hosting a newly discovered exoplanet with a radius of 1.12 RJupiter in a 3.9 day orbit.

 

 

Hu, R., 2010, "Transport of the First Rocks of the Solar System by X-winds," The Astrophysical Journal, 725, 1421-1428.

 

       It has been suggested that chondrules and calcium-aluminum-rich inclusions (CAIs) were formed at the inner edge of the protoplanetary disk and then entrained in magnetocentrifugal X-winds. We study trajectories of such solid bodies with the consideration of the central star gravity, the protoplanetary disk gravity, and the gas drag of the wind. The efficiency of the gas drag depends on a parameter ?, which is the product of the solid body size and density. We find that the gravity of the protoplanetary disk has a non-negligible effect on the trajectories. If a solid body re-enters the flared disk, the re-entering radius depends on the stellar magnetic dipole moment, the disk's gravity, the parameter h, and the initial launching angle. The disk's gravity can make the re-entering radius lower by up to 30%. We find a threshold h, denoted as ht , for any particular configuration of the X-wind, below which the solid bodies will be expelled from the planetary system. ht sensitively depends on the initial launching angle, and also depends on the mass of the disk. Only the solid bodies with an h larger than but very close to ht can be launched to a re-entering radius larger than 1 AU. This size-sorting effect may explain why chondrules come with a narrow range of sizes within each chondritic class. In general, the size distributions of CAIs and chondrules in chondrites can be determined from the initial size distribution as well as the distribution over the initial launching angle.

 

 

Ibragimov, R.N., 2010, "Mechanism of Energy Transfers to Smaller Scales Within the Rotational Internal Wave Field," Mathematical Physics, Analysis and Geometry, 13, 331-355.

 

 We discuss the effect of the earth rotation on the two-triad interaction and the oceanic energy distribution processes that occur between five coupled internal gravity waves. The system we study is a two-triad test wave system consisting of an initial wave of the tidal M2 frequency interacting with four recipient waves forming two resonant triads. It is shown that the general mechanism of an arbitrarily large number of internal wave interactions can be described by three classes of interactions which we call the sum, middle and difference interaction classes. The four latitude singularities are distinguished for the particular case of five interacting waves and all three classes of resonant interactions are studied separately at those critical values. It is shown that the sum and difference interaction classes represent the latitude-inferior and latitude-predominant classes respectively. The phenomenon of coalescence of the middle and difference interaction classes is observed along latitude 48.25° N. It shown that at this value of latitude, the coalescence phenomenon provides the analogy between rotating and reflecting internal waves from slopes.

 

 

Ireland, M.J., Kraus, A., Martinache, F., Law, N., Hillenbrand, L.A., 2011, "Two Wide Planetary-mass Companions to Solar-type Stars in Upper Scorpius," The Astrophysical Journal, 726, 113.

 

At wide separations, planetary-mass and brown dwarf companions to solar-type stars occupy a curious region of parameter space not obviously linked to binary star formation or solar system scale planet formation. These companions provide insight into the extreme case of companion formation (either binary or planetary), and due to their relative ease of observation when compared to close companions, they offer a useful template for our expectations of more typical planets. We present the results from an adaptive optics imaging survey for wide (~50-500 AU) companions to solar-type stars in Upper Scorpius. We report one new discovery of a ~14 MJ companion around GSC 06214.00210and confirm that the candidate planetary-mass companion 1RXS J160929.1.210524 detected by Lafreniè et al. is in fact comoving with its primary star. In our survey, these two detections correspond to ~4% of solar-type stars having companions in the 6-20 MJ mass and ~200-500 AU separation range. This figure is higher than would be expected if brown dwarfs and planetary-mass companions were drawn from an extrapolation of the binary mass function. Finally, we discuss implications for the formation of these objects.

 

 

Jenkins, J.M., Borucki, W.J., Koch, D.G., Marcy, G.W., Cochran, W.D., Welsh, W.F., Basri, G., Batalha, N.M., Buchhave, L.A., Brown, T.M., Caldwell, D.A., Dunham, E.W., Endl, M., Fischer, D.A., Gautier, T.N., Geary, J.C., Gilliland, R.L., Howell, S.B., Isaacson, H., Johnson, J.A., Latham, D.W., Lissauer, J.J., Monet, D.G., Rowe, J.F., Sasselov, D.D., Howard, A.W., MacQueen, P., Orosz, J.A., Chandrasekaran, H., Twicken, J.D., Bryson, S.T., Quintana, E.V., Clarke, B.D., Li, J., Allen, C., Tenenbaum, P., Wu, H., Meibom, S., Klaus, T.C., Middour, C.K., Cote, M.T., McCauliff, S., Girouard, F.R., Gunter, J.P., Wohler, B., Hall, J.R., Ibrahim, K., Kamal Uddin, A., Wu, M.S., Bhavsar, P.A., Van Cleve, J., Pletcher, D.L., Dotson, J.L., Haas, M.R., 2010, "Discovery and Rossiter-Mclaughlin Effect of Exoplanet Kepler-8b," The Astrophysical Journal, 724, 1108-1119.

 

 We report on the discovery and the Rossiter-McLaughlin (R-M) effect of Kepler-8b, a transiting planet identified by the NASA Kepler Mission. Kepler photometry and Keck-HIRES radial velocities yield the radius and mass of the planet around this F8IV subgiant host star. The planet has a radius RP= 1.419 RJ and a mass MP= 0.60 MJ, yielding a density of 0.26 g cm-3, one of the lowest planetary densities known. The orbital period is P = 3.523 days and the orbital semimajor axis is 0.0483+0.0006-0.0012 AU. The star has a large rotational vsin i of 10.5 ± 0.7 km s-1and is relatively faint (V »13.89 mag); both properties are deleterious to precise Doppler measurements. The velocities are indeed noisy, with scatter of 30 m s-1, but exhibit a period and phase that are consistent with those implied by transit photometry. We securely detect the R-M effect, confirming the planet's existence and establishing its orbit as prograde. We measure an inclination between the projected planetary orbital axis and the projected stellar rotation axis of l= -26fdg4 ± 10fdg1, indicating a significant inclination of the planetary orbit. R-M measurements of a large sample of transiting planets from Kepler will provide a statistically robust measure of the true distribution of spin-orbit orientations for hot Jupiters around F and early G stars.

 

 

Ji, J., Jin, S., Tinney, C.G., 2011, "Forming Close-in Earth-like Planets Via a Collision-merger Mechanism in Late-stage Planet Formation," The Astrophysical Journal, 727, L5.

 

The large number of exoplanets found to orbit their host stars in very close orbits have significantly advanced our understanding of the planetary formation process. It is now widely accepted that such short-period planets cannot have formed in situ, but rather must have migrated to their current orbits from a formation location much farther from their host star. In the late stages of planetary formation, once the gas in the protoplanetary disk has dissipated and migration has halted, gas giants orbiting in the inner disk regions will excite planetesimals and planetary embryos, resulting in an increased rate of orbital crossings and large impacts. We present the results of dynamical simulations for planetesimal evolution in this later stage of planet formation. We find that a mechanism is revealed by which the collision-merger of planetary embryos can kick terrestrial planets directly into orbits extremely close to their parent stars.

 

 

Johansson, E.P.G., Mueller, J., Motschmann, U., 2011, "Interplanetary magnetic field orientation and the magnetospheres of close-in exoplanets," Astronomy and Astrophysics, 525, 117.

 

The abundance of exoplanets with orbits smaller than that of Mercury most likely implies that there are exoplanets exposed to a quasiparallel stellar-wind magnetic field. Many of the generic features of stellar-wind interaction depend on the existence of a non-zero perpendicular interplanetary magnetic field component. However, for closer orbits the perpendicular component becomes smaller and smaller. The resulting quasiparallel interplanetary magnetic field may imply new types of magnetospheres and interactions not seen in the solar system. We simulate the Venus-like interaction between a supersonic stellar wind and an Earth-sized, unmagnetized terrestrial planet with ionosphere, orbiting a Sun-like star at 0.2 AU. The importance of a quasiparallel stellar-wind interaction is then studied by comparing three simulation runs with different angles between stellar wind direction and interplanetary magnetic field. The plasma simulation code is a hybrid code, representing ions as particles and electrons as a massless, charge-neutralizing adiabatic fluid. Apart from being able to observe generic features of supersonic stellar-wind interaction we observe the following changes and trends when reducing the angle between stellar wind and interplanetary magnetic field 1) that a large part of the bow shock is replaced by an unstable quasiparallel bow shock; 2) weakening magnetic draping and pile-up; 3) the creation of a second, flanking current sheet due to the need for the interplanetary magnetic field lines to connect to almost antiparallel draped field lines; 4) stellar wind reaching deeper into the dayside ionosphere; and 5) a decreasing ionospheric mass loss. The speed of the last two trends seems to accelerate at low angles.

 

 

Kashi, A., Soker, N., 2011, "The outcome of the protoplanetary disk of very massive stars," New Astronomy, 16, 27-32.

 

We suggest that planets, brown dwarfs, and even low mass stars can be formed by fragmentation of protoplanetary disks around very massive stars (M >~ 100 MSun). We discuss how fragmentation conditions make the formation of very massive planetary systems around very massive stars favorable. Such planetary systems are likely to be composed of brown dwarfs and low mass stars of .0.1.0.3 MSun, at orbital separations of ~ few ×100.104 AU. In particular, scaling from solar-like stars suggests that hundreds of Mercury-like planets might orbit very massive stars at ~103 AU where conditions might favor liquid water. Such fragmentation objects can be excellent targets for the James Webb Space Telescope and other large telescopes working in the IR bands. We predict that deep observations of very massive stars would reveal these fragmentation objects, orbiting in the same orbital plane in cases where there are more than one object.

 

 

Kholshevnikov, K.V., Kuznetsov, E.D., 2010, "Stability of planetary systems with respect to masses," Celestial Mechanics and Dynamical Astronomy, 93.

 

The stability in the sense of Lagrange of the Sun-Jupiter-Saturn system and 47 UMa system with respect to masses on a time scale of 106 years was studied using the method of averaging and numerical methods. When the masses of Jupiter and Saturn increase by 20 times (approximately, more accurate value depends on a time-scale of stable motion), these planets can have close approaches. Close approaches appear when analyzing osculating elements; they are absent in the mean elements. A similar situation takes place in the case of 47 UMa and other exoplanetary systems. The study of Lagrange stability with respect to masses allows us to obtain upper limits for masses of extrasolar planets.

 

Kocsis, B., Tremaine, S., 2011, "Resonant relaxation and the warp of the stellar disc in the Galactic Centre," Monthly Notices of the Royal Astronomical Society, 3.

 

Observations of the spatial distribution and kinematics of young stars in the Galactic Centre can be interpreted as showing that the stars occupy one, or possibly two, discs of radii .0.05-0.5 pc. The most prominent ("clockwise") disc exhibits a strong warp: the normals to the mean orbital planes in the inner and the outer third of the disc differ by .60°. Using an analytical model based on Laplace-Lagrange theory, we show that such warps arise naturally and inevitably through vector resonant relaxation between the disc and the surrounding old stellar cluster.

 

 

Korenaga, J., 2010, "On the Likelihood of Plate Tectonics on Super-Earths: Does Size Matter?," The Astrophysical Journal, 725, L43-L46.

 

The operation of plate tectonics on Earth is essential to modulate its atmospheric composition over geological time and is thus commonly believed to be vital for planetary habitability at large. It has been suggested that plate tectonics is very likely for super-Earths, with or without surface water, because a planet with a larger mass tends to have sufficient convective stress to escape from the mode of stagnant-lid convection. Here, this suggestion is revisited on the basis of the recently developed scaling laws of plate-tectonic convection, which indicate that the planetary size plays a rather minor role and that the likelihood of plate tectonics is controlled largely by the presence of surface water.

 

 

 

Ková, G., Bakos, G.Á, Hartman, J.D., Torres, G., Noyes, R.W., Latham, D.W., Howard, A.W., Fischer, D.A., Johnson, J.A., Marcy, G.W., Isaacson, H., Sasselov, D.D., Stefanik, R.P., Esquerdo, G.A., Fernandez, J.M., Lár, B.B.J., Papp, I., Sá, P., 2010, "HAT-P-15b: A 10.9 Day Extrasolar Planet Transiting a Solar-type Star," The Astrophysical Journal, 724, 866-877.

 

We report the discovery of HAT-P-15b, a transiting extrasolar planet in the "period valley," a relatively sparsely populated period regime of the known extrasolar planets. The host star, GSC 2883-01687, is a G5 dwarf with V= 12.16. It has a mass of 1.01 ± 0.04 M Sun, radius of 1.08 ± 0.04 R Sun, effective temperature 5568 ± 90 K, and metallicity [Fe/H] = +0.22 ± 0.08. The planetary companion orbits the star with a period P = 10.863502 ± 0.000027 days, transit epoch Tc = 2454638.56019 ± 0.00048 (BJD), and transit duration 0.2285 ± 0.0015 days. It has a mass of 1.946 ± 0.066 MJ and radius of 1.072 ± 0.043 RJ yielding a mean density of 1.96 ± 0.22 g cm-3. At an age of 6.8+2.5-1.6 Gyr, the planet is H/He-dominated and theoretical models require about 2% (10 MEarth) worth of heavy elements to reproduce its measured radius. With an estimated equilibrium temperature of ~820 K during transit, and ~1000 K at occultation, HAT-P-15b is a potential candidate to study moderately cool planetary atmospheres by transmission and occultation spectroscopy.

 

Lanza, A.F., Bonomo, A.S., Pagano, I., Leto, G., Messina, S., Cutispoto, G., Moutou, C., Aigrain, S., Alonso, R., Barge, P., Deleuil, M., Fridlund, M., Silva-Valio, A., Auvergne, M., Baglin, A., Collier Cameron, A., 2011, "Photospheric activity, rotation, and star-planet interaction of the planet-hosting star CoRoT-6," Astronomy and Astrophysics, 525, 14.

 

 Context. The CoRoT satellite has recently discovered a hot Jupiter that transits across the disc of a F9 main-sequence star called CoRoT-6 with a period of 8.886 days.

 

Aims: We model the photospheric activity of the star and use the maps of the active regions to study stellar differential rotation and the star-planet interaction.

 

Methods: We apply a maximum entropy spot model to fit the optical modulation as observed by CoRoT during a uninterrupted interval of ~ 140 days. Photospheric active regions are assumed to consist of spots and faculae in a fixed proportion with solar-like contrasts.

 

Results: Individual active regions have lifetimes up to 30-40 days. Most of them form and decay within five active longitudes whose different migration rates are attributed to the stellar differential rotation for which a lower limit of DW/W = 0.12 ± 0.02 is obtained. Several active regions show a maximum of activity at a longitude lagging the subplanetary point by ~ 200° with the probability of a chance occurrence being smaller than 1 percent.

 

Conclusions: Our spot modelling indicates that the photospheric activity of CoRoT-6 could be partially modulated by some kind of star-planet magnetic interaction, while an interaction related to tides is highly unlikely because of the weakness of the tidal force.

 

 

Lazio, T.J.W., Shankland, P.D., Farrell, W.M., Blank, D.L., 2010, "Radio Observations of HD 80606 Near Planetary Periastron," The Astronomical Journal, 140, 1929-1933.

 

This paper reports Very Large Array observations at 325 and 1425 MHz (l90 cm and l 20 cm) during and near the periastron passage of HD 80606b on HJD 2454424.86 (2007 November 20). We obtain flux density limits (3s) of 1.7 mJy and 48 mJy at 325 and 1425 MHz, respectively, equivalent to planetary luminosity limits of 2.3 ×1024 erg s-1and 2.7 ×1023 erg s-1. Unfortunately, these are several orders of magnitude above the nominal Jovian value (at 40 MHz) of 2 ×1018 erg s-1. The motivation for these observations was that the planetary magnetospheric emission is driven by a stellar wind-planetary magnetosphere interaction so that the planetary luminosity would be elevated near periastron. We estimate that, near periastron, HD 80606b might be as much as 3000 times more luminous than Jupiter. Recent transit observations of HD 80606b provide reasonably stringent constraints on the planetary mass and radius, and, because of the planet's highly eccentric orbit, its rotation period is likely to be "pseudo-synchronized" to its orbital period, allowing a robust estimate of the former. Consequently, we are able to make relatively robust estimates of the emission frequency of the planetary magnetospheric emission and find it to be around 60-90 MHz. While this is too low for our reported observations, we compare HD 80606b to other high-eccentricity systems and assess the detection possibilities for both near-term and more distant future systems. Of the known high-eccentricity planets, only HD 80606b is likely to be detectable, as the others (HD 20782B and HD 4113) are both lower mass and longer rotational periods, which imply weaker magnetic field strengths. We find that both the forthcoming "EVLA low band" system, which will operate as low as 65 MHz, and the Low Frequency Array may be able to improve upon our planetary luminosity limits for HD 80606b, and do so at a more optimum frequency. If the low-frequency component of the Square Kilometre Array (SKA-lo) and a future lunar radio array are able to approach their thermal noise limits, they should be able to detect an HD 80606b-like planet, unless the amount by which the planet's luminosity increases is substantially less than the factor of 3000 that we estimate; for the SKA-lo, which is to be located in the southern hemisphere, future planetary surveys will have to find southern hemisphere equivalents of HD 80606b.

 

Marcus, S.L., de Viron, O., Dickey, J.O., 2010, "Interannual atmospheric torque and El Niñouthern Oscillation: Where is the polar motion signal?," Journal of Geophysical Research (Solid Earth), 115, 12409.

 

In this paper, we investigate the atmospheric excitation of polar motion (PM) associated with the El Niñouthern Oscillation (ENSO) phenomenon. ENSO effects on length-of-day due to changes in the axial component of atmospheric angular momentum (AAM) have long been recognized, but identification of PM excitation with ENSO-induced equatorial AAM anomalies has proved more elusive. Here we use an appropriately modified form of the inverted barometer (IB) assumption to study ENSO-related atmospheric torques arising from pressure loading on the Earth's ellipsoidal bulge and mountains and from frictional wind stress over the Earth's land- and ocean-covered surface. The resulting dissipation torques, which accommodate adjustment of the oceanic mass distribution to time-variable atmospheric loading, are found to be small. The ellipsoidal torques have the largest amplitude, reflecting the order-of-magnitude discrepancy between the height departures of the Earth's bulge (~20 km) and its surface orography (~2 km). Because of relatively uniform pressure covariances with the Southern Oscillation Index over the continents for the largely land-based X component and the uniform IB response for the largely ocean-based Y component; however, the ENSO-related PM excitation arising from the ellipsoidal torques is reduced to an amplitude comparable with the sum of regional mountain torques from the individual continents. The largest of these are generated over Asia and Antarctica, arising from efficient coupling of ENSO-related surface pressure anomalies with large-scale orographic features. The geometrical mitigation of the ellipsoidal torques, classically expected to dominate equatorial AAM forcing, accounts for the lack of a detectable atmosphere-driven polar motion response to ENSO.

 

 

Marois, C., Zuckerman, B., Konopacky, Q.M., Macintosh, B., Barman, T., 2010, "Images of a fourth planet orbiting HR 8799," Nature, 468, 1080-1083.

 

High-contrast near-infrared imaging of the nearby star HR 8799 has shown three giant planets. Such images were possible because of the wide orbits (>25astronomical units, where 1AU is the Earth-Sun distance) and youth (<100Myr) of the imaged planets, which are still hot and bright as they radiate away gravitational energy acquired during their formation. An important area of contention in the exoplanet community is whether outer planets (>10AU) more massive than Jupiter form by way of one-step gravitational instabilities or, rather, through a two-step process involving accretion of a core followed by accumulation of a massive outer envelope composed primarily of hydrogen and helium. Here we report the presence of a fourth planet, interior to and of about the same mass as the other three. The system, with this additional planet, represents a challenge for current planet formation models as none of them can explain the in situ formation of all four planets. With its four young giant planets and known cold/warm debris belts, the HR 8799 planetary system is a unique laboratory in which to study the formation and evolution of giant planets at wide (>10AU) separations.

 

 

Matsumura, S., Peale, S.J., Rasio, F.A., 2010, "Tidal Evolution of Close-in Planets," The Astrophysical Journal, 725, 1995-2016.

 

Recent discoveries of several transiting planets with clearly non-zero eccentricities and some large obliquities started changing the simple picture of close-in planets having circular and well-aligned orbits. The two major scenarios that form such close-in planets are planet migration in a disk and planet-planet interactions combined with tidal dissipation. The former scenario can naturally produce a circular and low-obliquity orbit, while the latter implicitly assumes an initially highly eccentric and possibly high-obliquity orbit, which are then circularized and aligned via tidal dissipation. Most of these close-in planets experience orbital decay all the way to the Roche limit as previous studies showed. We investigate the tidal evolution of transiting planets on eccentric orbits, and find that there are two characteristic evolution paths for them, depending on the relative efficiency of tidal dissipation inside the star and the planet. Our study shows that each of these paths may correspond to migration and scattering scenarios. We further point out that the current observations may be consistent with the scattering scenario, where the circularization of an initially eccentric orbit occurs before the orbital decay primarily due to tidal dissipation in the planet, while the alignment of the stellar spin and orbit normal occurs on a similar timescale to the orbital decay largely due to dissipation in the star. We also find that even when the stellar spin-orbit misalignment is observed to be small at present, some systems could have had a highly misaligned orbit in the past, if their evolution is dominated by tidal dissipation in the star. Finally, we also re-examine the recent claim by Levrard et al. that all orbital and spin parameters, including eccentricity and stellar obliquity, evolve on a similar timescale to orbital decay. This counterintuitive result turns out to have been caused by a typo in their numerical code. Solving the correct set of tidal equations, we find that the eccentricity behaves as expected, with orbits usually circularizing rapidly compared to the orbital decay rate.

 

 

Maxted, P.F.L., Anderson, D.R., Gillon, M., Hellier, C., Queloz, D., Smalley, B., Triaud, A.H.M.J., West, R.G., Wilson, D.M., Bentley, S.J., Cegla, H., Collier Cameron, A., Enoch, B., Hebb, L., Horne, K., Irwin, J., Lister, T.A., Mayor, M., Parley, N., Pepe, F., Pollacco, D., Segransan, D., Udry, S., Wheatley, P.J., 2010, "WASP-22 b: A Transiting "Hot Jupiter" Planet in a Hierarchical Triple System," The Astronomical Journal, 140, 2007-2012.

 

We report the discovery of a transiting planet orbiting the star TYC 6446-326-1. The star, WASP-22, is a moderately bright (V = 12.0) solar-type star (Teff= 6000 ± 100 K, [Fe/H] = -0.05 ± 0.08). The light curve of the star obtained with the WASP-South instrument shows periodic transit-like features with a depth of about 1% and a duration of 0.14 days. The presence of a transit-like feature in the light curve is confirmed using z-band photometry obtained with Faulkes Telescope South. High-resolution spectroscopy obtained with the CORALIE and HARPS spectrographs confirms the presence of a planetary mass companion with an orbital period of 3.533 days in a near-circular orbit. From a combined analysis of the spectroscopic and photometric data assuming that the star is a typical main-sequence star we estimate that the planet has a mass M P= 0.56 ± 0.02M Jup and a radius R P= 1.12 ± 0.04RJup. In addition, there is a linear trend of 40 m s-1yr-1in the radial velocities measured over 16 months, from which we infer the presence of a third body with a long-period orbit in this system. The companion may be a low mass M-dwarf, a white dwarf, or a second planet.

 

 

Meru, F., Bate, M.R., 2010, "Non-convergence of the critical cooling time-scale for fragmentation of self-gravitating discs," Monthly Notices of the Royal Astronomical Society, L174.

 

       We carry out a resolution study on the fragmentation boundary of self-gravitating discs. We perform three-dimensional Smoothed Particle Hydrodynamics simulations of discs to determine whether the critical value of the cooling time-scale in units of the orbital time-scale, bcrit, converges with increasing resolution. Using particle numbers ranging from 31 250 to 16 million (the highest resolution simulations to date) we do not find convergence. Instead, fragmentation occurs for longer cooling time-scales as the resolution is increased. These results suggest that at the very least, the critical value of the cooling time-scale is longer than previously thought. However, the absence of convergence also raises the question of whether or not a critical value exists. In light of these results, we caution against using cooling time-scale or gravitational stress arguments to deduce whether gravitational instability may or may not have been the formation mechanism for observed planetary systems.

 

 

Mohler, M., Bü., Doherty, S., Eggl, S., Eybl, V.T., Farago, F., Ja?imovi?, A., Hunger, L., Lauritsen, N.L.B., Ludena, D., Meisnar, M., Reissner, A., Sarda, N., Toullec, B., Tió.V., 2010, "Opening a new window to other worlds with spectropolarimetry," Experimental Astronomy, 28, 101-135.

 

       A high level of diversity has already been observed among the planets of our own Solar System. As such, one expects extrasolar planets to present a wide range of distinctive features, therefore the characterisation of Earth- and super Earth-like planets is becoming of key importance in scientific research. The S earch ( Spectropolarimetric Exoplanet Atmosphe Re CHaracerisation) mission proposal of this paper represents one possible approach to realising these objectives. The mission goals of S earch include the detailed characterisation of a wide variety of exoplanets, ranging from terrestrial planets to gas giants. More specifically, S earch will determine atmospheric properties such as cloud coverage, surface pressure and atmospheric composition, and may also be capable of identifying basic surface features. To resolve a planet with a semi major axis of down to 1.4 AU and 30 pc distant S earch will have a mirror system consisting of two segments, with elliptical rim, cut out of a parabolic mirror. This will yield an effective diameter of 9 m along one axis. A phase mask coronagraph along with an integral spectrograph will be used to overcome the contrast ratio of star to planet light. Such a mission would provide invaluable data on the diversity present in extrasolar planetary systems and much more could be learned from the similarities and differences compared to our own Solar System. This would allow our theories of planetary formation, atmospheric accretion and evolution to be tested, and our understanding of regions such as the outer limit of the Habitable Zone to be further improved.

 

 

Molaro, P., CenturióM., 2011, "Ceres' sunlight atlas," Astronomy and Astrophysics, 525, 74.

 

Context. Astronomical research dealing with accurate radial velocity measurements need reliable astronomical standards to calibrate the spectrographs and to assess possible systematics. Stellar radial velocity standards offer a reference at the level of a few hundred m s-1and are not adequate for most present needs.

 

Aims: We aim to show that sunlight reflected by asteroids is a fairly accessible way to record a high-resolution solar spectrum from the whole disk, which can therefore be used as a radial velocity standard and can improve the uncertainties of solar line positions.

 

Methods: We used solar light reflected by the asteroid Ceres observed with HARPS to measure solar lines' wavelengths.

 

Results: We provide a new solar atlas with 491 line wavelengths in the range 540-690 nm and 222 lines in the range 400-410 nm obtained from reflected solar spectrum of Ceres. These measurements are consistent with those of Allende Prieto & Garcia Lopez (1998b) based on FTS solar atlases but with a factor 3 higher precision.

 

Conclusions: This atlas provides a benchmark for wavelength calibration to check radial velocity accuracy down to 44 m s-1locally and a few m s-1globally. The asteroid-based technique could provide a new way to track radial velocity shifts with solar activity cycle, as well as to derive convective shifts suitable for comparison with theoretical atmospheric models. It could also be used to study radial velocity deviations in spectrographs such as those recently detected in HIRES and UVES. Dedicated HARPS observations of other asteroids could improve present results substantially and these investigations have been solicited. Full Table 2 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/525/A74

 

 

Morais, M.H.M., Correia, A.C.M., 2011, "Stellar wobble caused by a nearby binary system: eccentric and inclined orbits," Astronomy and Astrophysics, 525, 152.

 

Most extrasolar planets currently known were discovered by means of an indirect method that measures the stellar wobble caused by the planet. We previously studied a triple system composed of a star and a nearby binary on circular coplanar orbits. We showed that although the effect of the binary on the star can be differentiated from the stellar wobble caused by a planet, because of observational limitations the two effects may often remain indistinguishable. Here, we develop a model that applies to eccentric and inclined orbits. We show that the binary's effect is more likely to be mistaken by planet(s) in the case of coplanar motion observed equator-on. Moreover, when the orbits are eccentric, the magnitude of the binary's effect may be larger than in the circular case. Additionally, an eccentric binary can mimic two planets with orbital periods in the ratio 2/1. However, when the star's orbit around the binary's center of mass has a high eccentricity and a reasonably well-constrained period, it should be easier to distinguish the binary's effect from a planet.

 

 

Mü T.G., ?urech, J., Hasegawa, S., Abe, M., Kawakami, K., Kasuga, T., Kinoshita, D., Kuroda, D., Urakawa, S., Okumura, S., Sarugaku, Y., Miyasaka, S., Takagi, Y., Weissman, P.R., Choi, Y.-J., Larson, S., Yanagisawa, K., Nagayama, S., 2011, "Thermo-physical properties of 162173 (1999 JU3), a potential flyby and rendezvous target for interplanetary missions," Astronomy and Astrophysics, 525, 145.

 

Context. Near-Earth asteroid 162173 (1999 JU3) is a potential flyby and rendezvous target for interplanetary missions because of its easy-to-reach orbit. The physical and thermal properties of the asteroid are relevant for establishing the scientific mission goals and also important in the context of near-Earth object studies in general.

 

Aims: Our goal was to derive key physical parameters such as shape, spin-vector, size, geometric albedo, and surface properties of 162173 (1999 JU3).

 

Methods: With three sets of published thermal observations (ground-based N-band, Akari IRC, Spitzer IRS), we applied a thermophysical model to derive the radiometric properties of the asteroid. The calculations were performed for the full range of possible shape and spin-vector solutions derived from the available sample of visual lightcurve observations.

 

Results: The near-Earth asteroid 162173 (1999 JU3) has an effective diameter of 0.87 ± 0.03 km and a geometric albedo of 0.070 ± 0.006. The c2-test reveals a strong preference for a retrograde sense of rotation with a spin-axis orientation of lecl = 73°, becl = -62° and Psid = 7.63 ± 0.01 h. The most likely thermal inertia ranges between 200 and 600 J m-2s-0.5 K-1, about a factor of 2 lower than the value for 25143 Itokawa. This indicates that the surface lies somewhere between a thick-dust regolith and a rock/boulder/cm-sized, gravel-dominated surface like that of 25143 Itokawa. Our analysis represents the first time that shape and spin-vector information has been derived from a combined data set of visual lightcurves (reflected light) and mid-infrared photometry and spectroscopy (thermal emission).

 

 

Nakada, M., 2011, "Earth's rotational variations due to rapid surface flows at both boundaries of the outer core," Geophysical Journal International, 184, 235-246.

 

 Rapid geomagnetic fluctuations with periods less than a couple of years, so called geomagnetic jerks, are coincident with sharp changes in rate of change of Earth's length of day (LOD) and phase of the Chandler wobble. Here I examine the rotational variations in response to sudden changes of toroidal core surface flows for geomagnetic jerks, assuming rigid rotation of the outer core and core surface flows at both boundaries (CMB and ICB) with the magnitude of ~3 km yr-1. I take into account the gravitational torque acting on the inner core associated with convective processes in the mantle and the electromagnetic (EM) coupling for a model with conductivity of the core of 5 ×105 S m-1and a 200 m conducting layer of 5 ×105 S m-1at the bottom of the mantle. The present study indicates that rapid accelerations of the flow at the CMB can produce LOD change consistent with observed LOD derivative with ~0.1 ms yr-1, but do not produce much for the polar motion. On the other hand, rapid accelerations of the flow at the ICB insignificantly affect the LOD change, but can produce polar motion signals that might affect the Chandler wobble if we adopt the EM coupling for a model with the flows of ~3 km yr-1and root-mean-square value of 4~5 mT for the radial magnetic field at the ICB.

 

 

Nelson, R.P., Gressel, O., 2010, "On the dynamics of planetesimals embedded in turbulent protoplanetary discs," Monthly Notices of the Royal Astronomical Society, 409, 639-661.

 

Angular momentum transport and accretion in protoplanetary discs are generally believed to be driven by magnetohydrodynamics (MHD) turbulence via the magnetorotational instability (MRI). The dynamics of solid bodies embedded in such discs (dust grains, boulders, planetesimals and planets) may be strongly affected by the turbulence, such that the formation pathways for planetary systems are determined in part by the strength and spatial distribution of the turbulent flow. We examine the dynamics of planetesimals, with radii between 1m and 10 km, embedded in turbulent protoplanetary discs, using 3D MHD simulations. The planetesimals experience gas drag and stochastic gravitational forces due to the turbulent disc. We use, and compare the results from, local shearing box simulations and global models in this study. The main aims of this work are to examine: the growth, and possible saturation, of the velocity dispersion of embedded planetesimals as a function of their size and disc parameters; the rate of radial migration and diffusion of planetesimals; the conditions under which the results from shearing box and global simulations agree. We find good agreement between local and global simulations when shearing boxes of dimension 4H ×16H ×2H are used (H being the local scale height). The magnitude of the density fluctuations obtained is sensitive to the box size, due to the excitation and propagation of spiral density waves. This affects the stochastic forcing experienced by planetesimals. The correlation time associated with the stochastic forcing is also found to be a function of the box size and aspect ratio. The equilibrium radial velocity dispersion, s(vr), obtained depends on the radii, RP, of the planetesimals. Bodies with RP= 50m achieve the smallest value with s(vr) ~= 20ms-1. Smaller bodies are tightly coupled to the gas, and boulders with RP = 1m attain a value of s(vr) similar to the turbulent velocity of the gas (~100ms-1). Equilibrium values of s(vr) for bodies larger than 100m are not achieved in our simulations, but in all models we find rapid growth of the velocity dispersion for planetesimals of size 1 and 10km, such that s(vr) >= 160ms-1after a run time of 1200 orbits at a distance of 5au from the central star. These values are too large to allow for the runaway growth of planetesimals, and mutual collisions would lead to catastrophic disruption. Radial migration due to gas drag is observed for bodies with RP~= 1m, and is only modestly affected by the turbulence. Larger bodies undergo a random walk in their semimajor axes, leading to radial diffusion through the disc. For our fiducial disc model, we estimate that radial diffusion across a distance of ~=2.5au would occur for typical planetesimals in a swarm located at 5au over a disc lifetime of 5Myr. Radial diffusion of this magnitude appears to be inconsistent with Solar system constraints. Our models show that fully developed magnetohydrodynamics (MHD) turbulence in protoplanetary discs would have a destructive effect on embedded planetesimals. Relatively low levels of turbulence are required for traditional models of planetesimal accretion to operate, this being consistent with the existence of a dead zone in protoplanetary discs.

 

 

Noordam, J.E., Smirnov, O.M., 2010, "The MeqTrees software system and its use for third-generation calibration of radio interferometers," Astronomy and Astrophysics, 524, 61.

 

Context. The formulation of the radio interferometer measurement equation (RIME) for a generic radio telescope by Hamaker et al. has provided us with an elegant mathematical apparatus for better understanding, simulation and calibration of existing and future instruments. The calibration of the new radio telescopes (LOFAR, SKA) would be unthinkable without the RIME formalism, and new software to exploit it.

 

Aims: The MeqTrees software system is designed to implement numerical models, and to solve for arbitrary subsets of their parameters. It may be applied to many problems, but was originally geared towards implementing Measurement Equations in radio astronomy for the purposes of simulation and calibration. The technical goal of MeqTrees is to provide a tool for rapid implementation of such models, while offering performance comparable to hand-written code. We are also pursuing the wider goal of increasing the rate of evolution of radio astronomical software, by offering a tool that facilitates rapid experimentation, and exchange of ideas (and scripts).

 

Methods: MeqTrees is implemented as a Python-based front-end called the meqbrowser, and an efficient (C++-based) computational back-end called the meqserver. Numerical models are defined on the front-end via a Python-based Tree Definition Language (TDL), then rapidly executed on the back-end. The use of TDL facilitates an extremely short turn-around time (hours rather than weeks or months) for experimentation with new ideas. This is also helped by unprecedented visualization capabilities for all final and intermediate results. A flexible data model and a number of important optimizations in the back-end ensures that the numerical performance is comparable to that of hand-written code.

 

Results: MeqTrees is already widely used as the simulation tool for new instruments (LOFAR, SKA) and technologies (focal plane arrays). It has demonstrated that it can achieve a noise-limited dynamic range in excess of a million, on WSRT data. It is the only package that is specifically designed to handle what we propose to call third-generation calibration (3GC), which is needed for the new generation of giant radio telescopes, but can also improve the calibration of existing instruments.

 

 

Nutzman, P., Gilliland, R.L., McCullough, P.R., Charbonneau, D., Christensen-Dalsgaard, J., Kjeldsen, H., Nelan, E.P., Brown, T.M., Holman, M.J., 2011, "Precise Estimates of the Physical Parameters for the Exoplanet System HD 17156 Enabled by Hubble Space Telescope Fine Guidance Sensor Transit and Asteroseismic Observations," The Astrophysical Journal, 726, 3.

 

We present observations of three distinct transits of HD 17156b obtained with the Fine Guidance Sensors on board the Hubble Space Telescope. We analyzed both the transit photometry and previously published radial velocities to find the planet-star radius ratio RP/Rêspan> = 0.07454 ± 0.00035, inclination i = 86.49+0.24.0.20 deg, and scaled semimajor axis a/ Rêspan> = 23.19+0.32.0.27. This last value translates directly to a mean stellar density determination êspan> = 0.522+0.021.0.018 g cm.3. Analysis of asteroseismology observations by the companion paper of Gilliland et al. provides a consistent but significantly refined measurement of rêspan>  = 0.5308 ± 0.0040. We compare stellar isochrones to this density estimate and find Mêspan>  = 1.275 ± 0.018 M Sun and a stellar age of 3.37+0.20.0.47 Gyr. Using this estimate of Mêspan>  and incorporating the density constraint from asteroseismology, we model both the photometry and published radial velocities to estimate the planet radius RP= 1.0870 ± 0.0066 RJand the stellar radius Rêspan>  = 1.5007 ± 0.0076 R Sun. The planet radius is larger than that found in previous studies and consistent with theoretical models of a solar-composition gas giant of the same mass and equilibrium temperature. For the three transits, we determine the times of mid-transit to a precision of 6.2 s, 7.6 s, and 6.9 s, and the transit times for HD 17156 do not show any significant departures from a constant period. The joint analysis of transit photometry and asteroseismology presages similar studies that will be enabled by the NASA Kepler Mission.

 

 

Ouyang, T., Yan, D., 2010, "Periodic solutions with alternating singularities in the collinear four-body problem," Celestial Mechanics and Dynamical Astronomy, 94.

 

This paper gives an analytic proof of the existence of Schubart-like orbit, a periodic orbit with singularities in the symmetric collinear four-body problem. In each period of the Schubart-like orbit, there is a binary collision (BC) between the inner two bodies and a simultaneous binary collision (SBC) of the two clusters on both sides of the origin. The system is regularized and the existence is proved by using a "turning point" technique and a continuity argument on differential equations of the regularized Hamiltonian.

 

 

Pá A., 2010, "Analysis of radial velocity variations in multiple planetary systems," Monthly Notices of the Royal Astronomical Society, 409, 975-984.

 

 By studying multiple extrasolar planetary systems, it is possible to obtain constraints for planetary masses and orbital inclinations using the detection of mutual perturbations. An analysis of precise radial velocity measurements might reveal these planet-planet interactions and yield a more accurate view of such planetary systems. As in generic data modelling problems, a fit to radial velocity data series has a set of unknown parameters of which parametric derivatives have to be known by both the regression methods and the estimations for the uncertainties. In this paper, an algorithm is described that aids the computation of such derivatives when planetary perturbations are not neglected. The application of the algorithm is demonstrated for the planetary systems of HD 73526, HD 128311 and HD 155358. In addition to the functions related to radial velocity analysis, the actual implementation of the algorithm contains functions that compute spatial coordinates, velocities and barycentric coordinates for each planet. These functions aid the joint analysis of multiple transiting planetary systems, transit timing and/or duration variations or systems where the proper motion of the host star is also measured involving high precision astrometry. The practical implementation related to the above-mentioned problems features functions that make these types of investigation simple and effective.

 

 

Pasetto, S., Grebel, E.K., Berczik, P., Chiosi, C., Spurzem, R., 2011, "Orbital evolution of the Carina dwarf galaxy and self-consistent determination of star formation history," Astronomy and Astrophysics, 525, 99.

 

We present a new study of the evolution of the Carina dwarf galaxy that includes a simultaneous derivation of its orbit and star formation history. The structure of the galaxy is constrained through orbital parameters derived from the observed distance, proper motions, radial velocity, and star formation history. The different orbits admitted by the large proper motion errors are investigated in relation to the tidal force exerted by an external potential representing the Milky Way. Our analysis is performed with the aid of fully consistent N-body simulations that are able to follow the dynamics and the stellar evolution of the dwarf system in order to determine the star formation history of Carina self-consistently. We also find a star formation history characterized by several bursts, partially matching the observational expectation. We find also compatible results between dynamical projected quantities and the observational constraints. The possibility of a past interaction between Carina and the Magellanic Clouds is also separately considered and deemed unlikely. Appendices are only available in electronic form at http://www.aanda.org

 

 

Pelat, D., Rouan, D., Pickel, D., 2010, "The achromatic chessboard, a new concept of a phase shifter for nulling interferometry. II. Theoretical performance assessment," Astronomy and Astrophysics, 524, 80.

 

Context. Nulling interferometry in the mid-IR using two telescopes (commonly referred to a Bracewell interferometer) is one possible way of directly detecting exoplanets in the habitable zone and their characterisation in terms of possible life signatures. A large wavelength domain is needed to simultaneously detect the infrared spectral features of a set of a bio-tracers. An achromatic phase shift of p is then required, and we previously presented a new concept for such a function that allows a simple design with only one device per beam. It is based on two cellular mirrors, called the chessboards, where each cell has a thickness that introduces, for any given central wavelength, a phase shift of (2k + 1) p or of 2kp on the fraction of the wave it reflects.

 

 Aims: We explore a more rigorous way to establish the optimum cell pattern design to attain the best theoretical performances for planet detection over a broad wavelength range. Two possible types of interferometers are now considered: on-axis and multi-axis.

 

Methods: We derived a rather simple iterative scheme for both designs, determining the thickness and XY position of the cells. The method confers to the chessboards a high degree of internal symmetry. Each design can be described as an iterative Bracewell interferometer characterised by an integer order. We demonstrate that their efficiencies increases with the power of that order.

 

Results: The device acts both spatially and versus wavelengths as an optical differential operator on the 3D light distribution. Its power is best understood in the on-axis case since its effect is to push away the stellar light from the centre over a very broad range of wavelengths, leaving space for an out of phase object to appear in the cleaned central region. We explore the theoretical performances for on-axis and multi-axis designs in the parameter space, and we especially compute the rejection factor for starlight and the attenuation factor for planet light and introduce the relative nulling efficiency metric. We show that, even with some realistic piston error added, the performances could meet the Darwin space project specifications for both designs, i.e., cancellation of the starlight by a factor of 105 over a wavelength range of 6-17 mm.

 

 

Pence, W.D., Chiappetti, L., Page, C.G., Shaw, R.A., Stobie, E., 2010, "Definition of the Flexible Image Transport System (FITS), version 3.0," Astronomy and Astrophysics, 524, 42.

 

The Flexible Image Transport System (FITS) has been used by astronomers for over 30 years as a data interchange and archiving format; FITS files are now handled by a wide range of astronomical software packages. Since the FITS format definition document (the .standard.) was last printed in this journal in 2001, several new features have been developed and standardized, notably support for 64-bit integers in images and tables, variable-length arrays in tables, and new world coordinate system conventions which provide a mapping from an element in a data array to a physical coordinate on the sky or within a spectrum. The FITS Working Group of the International Astronomical Union has therefore produced this new version 3.0 of the FITS standard, which is provided here in its entirety. In addition to describing the new features in FITS, numerous editorial changes were made to the previous version to clarify and reorganize many of the sections. Also included are some appendices which are not formally part of the standard. The FITS standard is likely to undergo further evolution, in which case the latest version may be found on the FITS Support Office Web site at http://fits.gsfc.nasa.gov/, which also provides many links to FITS-related resources.

 

Perryman, M.A.C., Schulze-Hartung, T.-., 69120 Heidelberg, Germany?%+ AA, AB, 2011, "The barycentric motion of exoplanet host stars. Tests of solar spin-orbit coupling," Astronomy and Astrophysics, 525, 65.

 

Context. Empirical evidence suggests a tantalizing but unproven link between various indicators of solar activity and the barycentric motion of the Sun. The latter is exemplified by transitions between regular and more disordered motion modulated by the motions of the giant planets, and rare periods of retrograde motion with negative orbital angular momentum. An examination of the barycentric motion of exoplanet host stars, and their stellar activity cycles, has the potential of proving or disproving the Sun's motion as an underlying factor in the complex patterns of short- and long-term solar variability indices, by establishing whether such correlations exist in other planetary systems. In either case, these studies may lead to further insight into the nature of the solar dynamo.

 

Aims: Some 40 multiple exoplanet systems are now known, all with reasonably accurate orbital elements. The forms and dynamical functions of the barycentric motion of their host stars are examined. These results can be compared with long-term activity indicators of exoplanet host stars, as they become available, to examine whether the correlations claimed for the Sun also exist in other systems.

 

Methods: Published orbital elements of multiple exoplanetary systems are used to examine their host star barycentric motions. For each system, we determine analytically the orbital angular momentum of the host star, and its rate of change.

 

Results: A variety of complex patterns of barycentric motions of exoplanet host stars is demonstrated, depending on the number, masses and orbits of the planets. Each of the behavioural types proposed to correlate with solar activity are also evident in exoplanet host stars: repetitive patterns influenced by massive multiple planets, epochs of rapid change in orbital angular momentum, and intervals of negative orbital angular momentum.

 

Conclusions: The study provides the basis for independent investigations of the widely-studied but unproven suggestion that the Sun's motion is somehow linked to various indicators of solar activity. We show that, because of the nature of their barycentric motions, the host stars HD 168443 and HD 74156 offer particularly powerful tests of this hypothesis.

 

 

Pires Dos Santos, P.M., Giuliatti Winter, S.M., Sfair, R., 2011, "Gravitational effects of Nix and Hydra in the external region of the Pluto-Charon system," Monthly Notices of the Royal Astronomical Society, 410, 273-279.

 

Two new companions to the Pluto-Charon binary system have been detected in 2005 by Weaver et al. These small satellites, named Nix and Hydra, are located beyond Charon's orbit. Although they are small when compared to Charon, their gravitational perturbations can decrease the stability of the external region (beyond Charon's orbit). The dynamical structure of this external region is analysed by numerically simulating a sample of particles under the gravitational effects of Pluto, Charon, Nix and Hydra. As expected the effects of Nix and Hydra decrease the external stable region. Agglomerates of particles can survive even after 105 orbital periods of the binary in some regions, such as coorbital to Nix and Hydra and between their orbits. We also analysed the effects of hypothetical satellites on the orbital evolution of Nix and Hydra in order to constrain an upper limit size. Some hypothetical satellites can be coorbital to Nix or Hydra without provoking any significant gravitational effects on them.

 

 

Rein, H., Papaloizou, J.C.B., 2010, "Stochastic orbital migration of small bodies in Saturn's rings," Astronomy and Astrophysics, 524, 22.

 

Many small moonlets that create propeller structures have been found in Saturn's rings by the Cassini spacecraft. We study the dynamical evolution of such 20-50 m sized bodies, which are embedded in Saturn's rings. We estimate the importance of various interaction processes with the ring particles on the moonlet's eccentricity and semi-major axis analytically. For low ring surface densities, the main effects on the evolution of the eccentricity and the semi-major axis are found to be caused by collisions and the gravitational interaction with particles in the vicinity of the moonlet. For high surface densities, the gravitational interaction with self-gravity wakes becomes important. We also perform realistic three-dimensional, collisional N-body simulations with up to a quarter of a million particles. A new set of pseudo shear periodic boundary conditions is used, which reduces the computational costs by an order of magnitude compared to previous studies. Our analytic estimates are confirmed to within a factor of two. On short timescales the evolution is always dominated by stochastic effects caused by collisions and gravitational interaction with self-gravitating ring particles. These result in a random walk of the moonlet's semi-major axis. The eccentricity of the moonlet quickly reaches an equilibrium value owing to collisional damping. The average change in semi-major axis of the moonlet after 100 orbital periods is 10-100m. This translates to an offset in the azimuthal direction of several hundred kilometres. We expect that such a shift is easily observable. Two movies are only available in electronic form at http://www.aanda.org

 

 

Riaz, B., Martí E.L., 2011, "Large-amplitude photometric variability of the candidate protoplanet TMR-1C," Astronomy and Astrophysics, 525, 10.

 

Context. TMR-1C is a candidate protoplanet that lies at a separation of about 10. (~1000 AU) from the Class I protobinary TMR-1 (IRAS 04361+2547) located in the Taurus molecular cloud. A narrow filament-like structure was observed in the discovery HST/NICMOS images, extending southeast from the central proto-binary system towards TMR-1C, suggesting a morphology in which the candidate protoplanet may have been ejected from the TMR-1 system. Follow-up low-resolution spectroscopy, however, could not confirm if this object is a protoplanet or a low-luminosity background star

 

Aims: We present two epochs of near-infrared photometric observations obtained at the CFHT of TMR-1C. The time span of ~7 years between the two sets of observations provides an opportunity to (a) check for any photometric variability similar to that observed among young stellar objects, which would indicate the youth of this source, and to (b) determine the proper motion.

 

Results: TMR-1C displays large photometric variability between 1 and 2 mag in both the H- and K<SUB>s</SUB>-bands. From our 2002 observations, we find a (H-Ks) color of 0.3 mag, which is much bluer than the value of 1.3 mag reported by T98 from HST observations. Also, we observe brightening in both the H- and Ks-bands when the colors are bluer; i.e., the object gets redder as it becomes fainter. We have explored the possible origins for the observed variability, and find extinction due to the presence of circumstellar material to be the most likely scenario. The observed large-amplitude photometric variations and the possible presence of a circumstellar disk are strong arguments against this object being an old background star.

 

 

Ryu, Y.-H., Chang, H.-Y., Park, M.-G., 2010, "Detection probability of a low-mass planet for triple lens events: implication of properties of binary-lens superposition," Monthly Notices of the Royal Astronomical Society, 1875.

 

 In view of the assumption that any planetary system is likely to be composed of more than one planet, and that a multiple planet system with a large-mass planet has a greater chance of detailed follow-up observations, the multiple planet system may be an efficient way to search for sub-Jovian planets. We study the central region of the magnification pattern for the triple lens system composed of a star, a Jovian mass planet and a low-mass planet to answer the question of if the low-mass planet can be detected in high-magnification events. We compare the magnification pattern of the triple lens system with that of a best-fitted binary system composed of a star and a Jovian mass planet, and check the probability of detecting the low-mass secondary planet whose signature will be superposed on that of the primary Jovian mass planet. Detection probabilities of the low-mass planet in the triple lens system are quite similar to the probability of detecting such a low-mass planet in a binary system with a star and only a low-mass planet, which shows that the signature of a low-mass planet can be effectively detected even when it is concurrent with the signature of the more massive planet, implying that the binary superposition approximation works over a relatively broad range of planet mass ratio and separations, and the inaccuracies thereof do not significantly affect the detection probability of the lower-mass secondary planet. Since the signature of the Jovian mass planet will be larger and lasting longer, thereby warranting more intensive follow-up observations, the actual detection rate of the low-mass planet in a triple system with a Jovian mass can be significantly higher than that in a binary system with a low-mass planet only. We conclude that it may be worthwhile to develop an efficient algorithm to search for `super-Earth' planets in the paradigm of the triple lens model for high-magnification microlensing events.

 

 

Sandell, G., Weintraub, D.A., Hamidouche, M., 2011, "A Submillimeter Mapping Survey of Herbig AeBe Stars," The Astrophysical Journal, 727, 26.

 

We have acquired submillimeter observations of 33 fields containing 37 Herbig Ae/Be (HAEBE) stars or potential HAEBE stars, including SCUBA maps of all but two of these stars. Nine target stars show extended dust emission. The other 18 are unresolved, suggesting that the dust envelopes or disks around these stars are less than a few arcseconds in angular size. In several cases, we find that the strongest submillimeter emission originates from younger, heavily embedded sources rather than from the HAEBE star, which means that previous models must be viewed with caution. These new data, in combination with far-infrared flux measurements available in the literature, yield spectral energy distributions (SEDs) from far-infrared to millimeter wavelengths for all the observed objects. Isothermal fits to these SEDs demonstrate excellent fits, in most cases, to the flux densities longward of 100 mm. We find that a smaller proportion of B-type stars than A- and F-type stars are surrounded by circumstellar disks, suggesting that disks around B stars dissipate on shorter timescales than those around later spectral types. Our models also reveal that the mass of the circumstellar material and the value of b are correlated, with low masses corresponding to low values of b. Since low values of b imply large grain sizes, our results suggest that a large fraction of the mass in low- b sources is locked up in very large grains. Several of the isolated HAEBE stars have disks with very flat submillimeter SEDs. These disks may be on the verge of forming planetary systems.

 

 

Shannon, R.M., Cordes, J.M., 2010, "Assessing the Role of Spin Noise in the Precision Timing of Millisecond Pulsars," The Astrophysical Journal, 725, 1607-1619.

 

We investigate rotational spin noise (referred to as timing noise) in non-accreting pulsars: millisecond pulsars, canonical pulsars, and magnetars. Particular attention is placed on quantifying the strength and non-stationarity of timing noise in millisecond pulsars because the long-term stability of these objects is required to detect nanohertz gravitational radiation. We show that a single scaling law is sufficient to characterize timing noise in millisecond and canonical pulsars while the same scaling law underestimates the levels of timing noise in magnetars. The scaling law, along with a detailed study of the millisecond pulsar B1937+21, leads us to conclude that timing noise is latent in most millisecond pulsars and will be measurable in many objects when better arrival time estimates are obtained over long data spans. The sensitivity of a pulsar timing array to gravitational radiation is strongly affected by any timing noise. We conclude that detection of proposed gravitational wave backgrounds will require the analysis of more objects than previously suggested over data spans that depend on the spectra of both the gravitational wave background and of the timing noise. It is imperative to find additional millisecond pulsars in current and future surveys in order to reduce the effects of timing noise.

 

 

Simpson, E.K., Faedi, F., Barros, S.C.C., Brown, D.J.A., Collier Cameron, A., Hebb, L., Pollacco, D., Smalley, B., Todd, I., Butters, O.W., Héard, G., McCormac, J., Miller, G.R.M., Santerne, A., Street, R.A., Skillen, I., Triaud, A.H.M.J., Anderson, D.R., Bento, J., Boisse, I., Bouchy, F., Enoch, B., Haswell, C.A., Hellier, C., Holmes, S., Horne, K., Keenan, F.P., Lister, T.A., Maxted, P.F.L., Moulds, V., Moutou, C., Norton, A.J., Parley, N., Pepe, F., Queloz, D., Segransan, D., Smith, A.M.S., Stempels, H.C., Udry, S., Watson, C.A., West, R.G., Wheatley, P.J., 2011, "WASP-37b: A 1.8 M J Exoplanet Transiting a Metal-poor Star," The Astronomical Journal, 141, 8.

 

We report on the discovery of WASP-37b, a transiting hot Jupiter orbiting an mv = 12.7 G2-type dwarf, with a period of 3.577469 ± 0.000011 d, transit epoch T0 = 2455338.6188 ± 0.0006 (HJD; dates throughout the paper are given in Coordinated Universal Time (UTC)), and a transit duration 0.1304+0.0018.0.0017 d. The planetary companion has a mass M P= 1.80 ± 0.17 MJ and radius RP= 1.16+0.07.0.06 RJ, yielding a mean density of 1.15+0.12.0.15 rJ. From a spectral analysis, we find that the host star has Mêspan> = 0.925 ± 0.120 M Sun, Rêspan> = 1.003 ± 0.053 R Sun, T eff = 5800 ± 150 K, and [Fe/H] = .0.40 ± 0.12. WASP-37 is therefore one of the lowest metallicity stars to host a transiting planet.

 

 

Singh, J., 2010, "Nonlinear stability in the restricted three-body problem with oblate and variable mass," Astrophysics and Space Science, 386.

 

This study investigates the nonlinear stability of the triangular equilibrium points when the bigger primary is an oblate spheroid and the infinitesimal body varies (decreases) it's mass in accordance with Jeans' law. It is found that these points are stable for all mass ratios in the range of linear stability except for three mass ratios depending upon oblateness coefficient A and b, a constant due to the variation in mass governed by Jeans' law.

 

 

Steffen, J.H., Batalha, N.M., Borucki, W.J., Buchhave, L.A., Caldwell, D.A., Cochran, W.D., Endl, M., Fabrycky, D.C., Fressin, F., Ford, E.B., Fortney, J.J., Haas, M.J., Holman, M.J., Howell, S.B., Isaacson, H., Jenkins, J.M., Koch, D., Latham, D.W., Lissauer, J.J., Moorhead, A.V., Morehead, R.C., Marcy, G., MacQueen, P.J., Quinn, S.N., Ragozzine, D., Rowe, J.F., Sasselov, D.D., Seager, S., Torres, G., Welsh, W.F., 2010, "Five Kepler Target Stars That Show Multiple Transiting Exoplanet Candidates," The Astrophysical Journal, 725, 1226-1241.

 

       We present and discuss five candidate exoplanetary systems identified with the Kepler spacecraft. These five systems show transits from multiple exoplanet candidates. Should these objects prove to be planetary in nature, then these five systems open new opportunities for the field of exoplanets and provide new insights into the formation and dynamical evolution of planetary systems. We discuss the methods used to identify multiple transiting objects from the Kepler photometry as well as the false-positive rejection methods that have been applied to these data. One system shows transits from three distinct objects while the remaining four systems show transits from two objects. Three systems have planet candidates that are near mean motion commensurabilities.two near 2:1 and one just outside 5:2. We discuss the implications that multi-transiting systems have on the distribution of orbital inclinations in planetary systems, and hence their dynamical histories, as well as their likely masses and chemical compositions. A Monte Carlo study indicates that, with additional data, most of these systems should exhibit detectable transit timing variations (TTVs) due to gravitational interactions, though none are apparent in these data. We also discuss new challenges that arise in TTV analyses due to the presence of more than two planets in a system.

 

 

Stock, N.D., Su, K.Y.L., Liu, W., Hinz, P.M., Rieke, G.H., Marengo, M., Stapelfeldt, K.R., Hines, D.C., Trilling, D.E., 2010, "The Structure of the b Leonis Debris Disk," The Astrophysical Journal, 724, 1238-1255.

 

       We combine nulling interferometry at 10 mm using the MMT and Keck Telescopes with spectroscopy, imaging, and photometry from 3 to 100 mm using Spitzer to study the debris disk around b Leo over a broad range of spatial scales, corresponding to radii of 0.1 to ~100 AU. We have also measured the close binary star o Leo with both Keck and MMT interferometers to verify our procedures with these instruments. The b Leo debris system has a complex structure: (1) relatively little material within 1 AU (2) an inner component with a color temperature of ~600 K, fitted by a dusty ring from about 2-3 AU and (3) a second component with a color temperature of ~120 K fitted by a broad dusty emission zone extending from about ~5 AU to ~55 AU. Unlike many other A-type stars with debris disks, b Leo lacks a dominant outer belt near 100 AU.

 

 

Team, T.G.P., Gendt, G., Altamimi, Z., Dach, R., Sö, W., Springer, T., 2011, "GGSP: Realisation and maintenance of the Galileo Terrestrial Reference Frame," Advances in Space Research, 47, 174-185.

 

The realisation and maintenance of a Galileo Terrestrial Reference Frame (GTRF) is the main function of the Galileo Geodetic Service Provider (GGSP). The GTRF shall be compatible with the latest International Terrestrial Reference Frame (ITRF) within a precision level of 3 cm (2 sigma). The connection to the ITRF is realized and validated by stations of the International GNSS Service (IGS) and by geodetic local ties to stations equipped with other geodetic techniques. It is demonstrated that this GTRF can be maintained by including the Galileo Signal-in-Space data, once Galileo reaches its operational stage.The GGSP will also provide additional products, such as Earth Rotation Parameters, satellites orbits, clock corrections for satellites and stations, which will be offered to the Galileo user community to have most precise access to the GTRF and will be used to monitor the accuracy of the corresponding Galileo Mission Segment.The GGSP was built up in time, and for a final demonstration the full system was operated for an interval of 6 months. During that time also microwave data from the two active GIOVE satellites were used.The GGSP Consortium followed the most up to date IGS standards of weekly processing during seven monthly campaigns (November 2006 to June 2008) and a continuous processing from September 2008 to February 2009 delivering several versions of the GTRF. The latest GTRF solution (GTRF09v01) has an RMS position difference with respect to the ITRF2005 computed over the 71 common stations of 1.1 and 2.9 mm in the horizontal and vertical components, respectively. The RMS velocity differences are 0.3 and 0.6 mm/y, respectively. The GGSP GPS satellite orbits and clock corrections agree with the IGS Final products at a level of 5.11 mm and 0.02.0.03 ns, respectively.The quality of the GIOVE orbits is at a level of 20.30 cm. The Hydrogen-Maser on board of GIOVE-B is nearly one order of magnitude better than the GPS satellite clocks.

 

 

Théult, P., Marzari, F., Augereau, J.-C., 2010, "Debris discs in binaries: a numerical study," Astronomy and Astrophysics, 524, 13.

 

Context. Debris disc analysis and modelling provide crucial information about the structure and the processes at play in extrasolar planetary systems. In binary systems, this issue is more complex because the disc should also respond to the companion star's perturbations.

 

Aims: We explore the dynamical evolution of a collisionally active debris disc for different initial parent body populations, diverse binary configurations, and optical depths. We focus on the radial extent and size distribution of the disc in a stationary state.

 

Methods: We numerically followed the evolution of 105 massless small grains, initially produced from a circumprimary disc of parent bodies following a size distribution in dN µ s-3.5ds . Grains were submitted to both stars' gravity and radiation pressure. In addition, particles were assigned an empirically derived collisional lifetime.

 

Results: For all the binary configurations, the disc extends far beyond the critical semi-major axis acrit for orbital stability. This is due to the steady production of small grains, placed by radiation pressure on eccentric orbits reaching beyond acrit . The amount of matter beyond acrit depends on the balance between collisional production and dynamical removal rates: it increases for more massive discs, as well as for eccentric binaries. Another important effect is that, in the dynamically stable region, the disc is depleted from its smallest grains. Both results could lead to observable signatures.

 

Conclusions: We have shown that a companion star can never fully truncate a collisionally active disc. For eccentric companions, grains in the unstable regions can contribute significantly to the thermal emission in the mid-IR. Discs with sharp outer edges, especially bright ones such as HR4796A, are probably shaped by other mechanisms.

 

 

Tingley, B., Bonomo, A.S., Deeg, H.J., 2011, "Using Stellar Densities to Evaluate Transiting Exoplanetary Candidates," The Astrophysical Journal, 726, 112.

 

One of the persistent complications in searches for transiting exoplanets is the low percentage of the detected candidates that ultimately prove to be planets, which significantly increases the load on the telescopes used for the follow-up observations to confirm or reject candidates. Several attempts have been made at creating techniques that can pare down candidate lists without the need of additional observations. Some of these techniques involve a detailed analysis of light curve characteristics; others estimate the stellar density or some proxy thereof. In this paper, we extend upon this second approach, exploring the use of independently calculated stellar densities to identify the most promising transiting exoplanet candidates. We use a set of CoRoT candidates and the set of known transiting exoplanets to examine the potential of this approach. In particular, we note the possibilities inherent in the high-precision photometry from space missions, which can detect stellar asteroseismic pulsations from which accurate stellar densities can be extracted without additional observations.

 

 

Torres, G., Fressin, F., Batalha, N.M., Borucki, W.J., Brown, T.M., Bryson, S.T., Buchhave, L.A., Charbonneau, D., Ciardi, D.R., Dunham, E.W., Fabrycky, D.C., Ford, E.B., Gautier, T.N., III, Gilliland, R.L., Holman, M.J., Howell, S.B., Isaacson, H., Jenkins, J.M., Koch, D.G., Latham, D.W., Lissauer, J.J., Marcy, G.W., Monet, D.G., Prsa, A., Quinn, S.N., Ragozzine, D., Rowe, J.F., Sasselov, D.D., Steffen, J.H., Welsh, W.F., 2011, "Modeling Kepler Transit Light Curves as False Positives: Rejection of Blend Scenarios for Kepler-9, and Validation of Kepler-9 d, A Super-earth-size Planet in a Multiple System," The Astrophysical Journal, 727, 24.

 

Light curves from the Kepler Mission contain valuable information on the nature of the phenomena producing the transit-like signals. To assist in exploring the possibility that they are due to an astrophysical false positive, we describe a procedure (BLENDER) to model the photometry in terms of a "blend" rather than a planet orbiting a star. A blend may consist of a background or foreground eclipsing binary (or star-planet pair) whose eclipses are attenuated by the light of the candidate and possibly other stars within the photometric aperture. We apply BLENDER to the case of Kepler-9 (KIC 3323887), a target harboring two previously confirmed Saturn-size planets (Kepler-9 b and Kepler-9 c) showing transit timing variations, and an additional shallower signal with a 1.59 day period suggesting the presence of a super-Earth-size planet. Using BLENDER together with constraints from other follow-up observations we are able to rule out all blends for the two deeper signals and provide independent validation of their planetary nature. For the shallower signal, we rule out a large fraction of the false positives that might mimic the transits. The false alarm rate for remaining blends depends in part (and inversely) on the unknown frequency of small-size planets. Based on several realistic estimates of this frequency, we conclude with very high confidence that this small signal is due to a super-Earth-size planet (Kepler-9 d) in a multiple system, rather than a false positive. The radius is determined to be 1.64+0.19.0.14 REarth and current spectroscopic observations are as yet insufficient to establish its mass.

 

 

Triaud, A.H.M.J., Collier Cameron, A., Queloz, D., Anderson, D.R., Gillon, M., Hebb, L., Hellier, C., Loeillet, B., Maxted, P.F.L., Mayor, M., Pepe, F., Pollacco, D., Séansan, D., Smalley, B., Udry, S., West, R.G., Wheatley, P.J., 2010, "Spin-orbit angle measurements for six southern transiting planets. New insights into the dynamical origins of hot Jupiters," Astronomy and Astrophysics, 524, 25.

 

Context. Several competing scenarios for planetary-system formation and evolution seek to explain how hot Jupiters came to be so close to their parent stars. Most planetary parameters evolve with time, making it hard to distinguish between models. The obliquity of an orbit with respect to the stellar rotation axis is thought to be more stable than other parameters such as eccentricity. Most planets, to date, appear aligned with the stellar rotation axis; the few misaligned planets so far detected are massive (> 2 MJ).

 

Aims: Our goal is to measure the degree of alignment between planetary orbits and stellar spin axes, to search for potential correlations with eccentricity or other planetary parameters and to measure long term radial velocity variability indicating the presence of other bodies in the system.

 

 Methods: For transiting planets, the Rossiter-McLaughlin effect allows the measurement of the sky-projected angle b between the stellar rotation axis and a planet's orbital axis. Using the HARPS spectrograph, we observed the Rossiter-McLaughlin effect for six transiting hot Jupiters found by the WASP consortium. We combine these with long term radial velocity measurements obtained with CORALIE. We used a combined analysis of photometry and radial velocities, fitting model parameters with the Markov Chain Monte Carlo method. After obtaining b we attempt to statistically determine the distribution of the real spin-orbit angle y.

 

Results: We found that three of our targets have b above 90°: WASP-2b: b = 153°+11-15, WASP-15b: b = 139.6°+5.2-4.3 and WASP-17b: b = 148.5°+5.1-4.2; the other three (WASP-4b, WASP-5b and WASP-18b) have angles compatible with 0°. We find no dependence between the misaligned angle and planet mass nor with any other planetary parameter. All six orbits are close to circular, with only one firm detection of eccentricity e = 0.00848+0.00085-0.00095 in WASP-18b. No long-term radial acceleration was detected for any of the targets. Combining all previous 20 measurements of b and our six and transforming them into a distribution of y we find that between about 45 and 85% of hot Jupiters have y > 30°.

 

Conclusions: Most hot Jupiters are misaligned, with a large variety of spin-orbit angles. We find observations and predictions using the Kozai mechanism match well. If these observational facts are confirmed in the future, we may then conclude that most hot Jupiters are formed from a dynamical and tidal origin without the necessity to use type I or II migration. At present, standard disc migration cannot explain the observations without invoking at least another additional process. Using observations with the high resolution éelle spectrograph HARPS mounted on the ESO 3.6 m (under proposals 072.C-0488, 082.C-0040 & 283.C-5017), and with the high resolution éelle spectrograph CORALIE on the 1.2 m Euler Swiss Telescope, both installed at the ESO La Silla Observatory in Chile.RV data is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/524/A25

 

 

Verdun, A., 2010, ""Astronomica" in the Correspondence between Leonhard Euler and Daniel Bernoull (German Title: "Astronomica" im Briefwechsel zwischen Leonhard Euler und Daniel Bernoulli)," Acta Historica Astronomiae, 41, 169-199.

 

The Euler Commission of the Swiss Academy of Sciences intends to terminate the edition of Leonhard Euler's works in the next year 2011 after nearly one hundred years since the beginning of the editorial works. These works include, e.g., Volume 3 of the Series quarta A which will contain the correspondence between Leonhard Euler (1707-1783) and Daniel Bernoulli (1700-1783) and which is currently being edited by Dr. Emil A. Fellmann (Basel) and Prof. Dr. Gleb K. Mikhailov (Moscow). This correspondence contains more than hundred letters, principally from Daniel Bernoulli to Euler. Parts of this correspondence were published uncommented already in 1843. It is astonishing that, apart from mathematics and physics (mainly mechanics and hydrodynamics), many topics addressed concern astronomy. The major part of the preserved correspondence between Euler and Daniel Bernoulli, in which astronomical themes are discussed, concerns celestial mechanics as the dominant discipline of theoretical astronomy of the eighteenth century. It was triggered and coined mainly by the prize questions of the Paris Academy of Science. In more than two thirds of the letters current problems and questions concerning celestial mechanics of that time are treated, focusing on the lunar theory and the great inequality in the motions of Jupiter and Saturn as special applications of the three body problem. In the remaining letters, problems concerning spherical astronomy are solved and attempts are made to explain certain phenomena in the field of "cosmic physics" concerning astronomical observations.

 

 

Xu, G., Tianhe, X., Chen, W., Yeh, T.-K., 2011, "Analytical solution of a satellite orbit disturbed by atmospheric drag," Monthly Notices of the Royal Astronomical Society, 410, 654-662.

 

In this paper, we derive the analytical solution of a satellite orbit disturbed by atmospheric drag. The disturbance force vector is first transformed and rotated to the orbital frame so that it can be used in the simplified Gaussian equations of satellite motion. Then, the force vector is expanded to triangular functions of the Keplerian angular elements and the disturbances are separated into three parts: short-periodic terms with triangular functions of M, long-periodic terms with triangular functions of (w, i) and secular terms [non-periodic functions of (a, e)] with a program using mathematical symbolic operation software. The integrations are then carried out with respect to M, (w, i) and t, respectively, to obtain the analytical solutions of satellite orbits disturbed by atmospheric drag. Some interesting conclusions are obtained theoretically. The atmospheric disturbance force is not a function of W. The semimajor axis a of the orbital ellipse is reduced in a constant and strong manner by the air disturbance; the shape of the ellipse (eccentricity e) changes towards a more circular orbit in a linear and weak manner. The right ascension of the ascending node W and the mean anomaly M are influenced by the disturbance only short periodically.

 

 

Xu, G., Xu, T., Yeh, T.-K., Chen, W., 2011, "Analytical solution of a satellite orbit disturbed by lunar and solar gravitation," Monthly Notices of the Royal Astronomical Society, 410, 645-653.

 

In this paper, we derive to the second order (5 ×10-6) the analytical solution of a satellite orbit disturbed by the lunar gravitational force. The force vector is first expanded to omit terms smaller than the third order (10-9). Then, four terms of potential functions are derived from the expanded force vector and set into the Lagrangian equations of satellite motion to obtain the theoretical solutions. For the first term of the potential functions, the solutions are derived directly. For the second term, mathematical expansions and transformations are used to separate disturbances into three parts: short-periodic terms with triangular functions of M, long-periodic terms with triangular functions of (w, i, W) and secular terms with non-periodic functions of (a, e). The integrations are then carried out with respect to M, (w, i, W) and t, to obtain the analytical solutions of satellite orbits with a program using mathematical symbolic operation software. The third potential function differs from the second by a factor and the fourth is simpler than the second. Therefore, the solutions are derived similarly using slightly modified programs, respectively. The results show that only two Keplerian elements (w, M) are linearly perturbed by lunar gravitation; that is, the lunar attracting force will cause a linear regression (delay) of the perigee (orientation of the ellipse) and a linear delay of the position (mean anomaly) on an Earth satellite. The Keplerian element a (semimajor axis of the ellipse) is not perturbed long periodically as the others. The derived solutions are also valid for solar and planetary gravitational disturbances. Because of the distance differences between the Moon, the Sun and the planets to the Earth or an Earth satellite, the solutions are of third and fourth orders for solar and planetary gravitational disturbances on an Earth satellite, respectively.

 

 

Yeager, K.E., Eberle, J., Cuntz, M., 2011, "On the ejection of Earth-mass planets from the habitable zones of the solar twins HD 20782 and HD 188015," International Journal of Astrobiology, 10, 1-13.

 

We provide a detailed statistical study of the ejection of fictitious Earth-mass planets from the habitable zones of the solar twins HD 20782 and HD 188015. These systems possess a giant planet that crosses into the stellar habitable zone, thus effectively thwarting the possibility of habitable terrestrial planets. In the case of HD 188015, the orbit of the giant planet is essentially circular, whereas in the case of HD 20782, it is extremely elliptical. As starting positions for the giant planets, we consider both the apogee and perigee positions, whereas the starting positions of the Earth-mass planets are widely varied. For the giant planets, we consider models based on their minimum masses as well as models where the masses are increased by 30%. Our simulations indicate a large range of statistical properties concerning the ejection of the Earth-mass planets from the stellar habitable zones. For example, it is found that the ejection times for the Earth-mass planets from the habitable zones of HD 20782 and HD 188015, originally placed at the centre of the habitable zones, vary by a factor of ~200 and ~1500, respectively, depending on the starting positions of the giant and terrestrial planets. If the mass of the giant planet is increased by 30%, the variation in ejection time for HD 188015 increases to a factor of ~6000. However, the short survival times of any Earth-mass planets in these systems are of no surprise. It is noteworthy, however, that considerable differences in the survival times of the Earth-mass planets are found, which may be relevant for establishing guidelines of stability for systems with less intrusive giant planets.